Slaughter the thundering i915_wait_request, v3?

Slaughter the thundering i915_wait_request, v3?

[Chris Wilson]

The biggest change is the revised bottom-half for handling user
interupts (now we use the waiter on the oldest request as the
bottom-half). That and the review feedback on Daniel on handling resets
(and hangcheck) during the wait. Oh, and some interrupt/seqno timing review.

Available from
http://cgit.freedesktop.org/~ickle/linux-2.6/log/?h=breadcrumbs
-Chris

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[PATCH 01/32] drm/i915: Break busywaiting for requests on pending signals

[Chris Wilson]

The busywait in __i915_spin_request() does not respect pending signals
and so may consume the entire timeslice for the task instead of
returning to userspace to handle the signal.

In the worst case this could cause a delay in signal processing of 20ms,
which would be a noticeable jitter in cursor tracking. If a higher
resolution signal was being used, for example to provide fairness of a
server timeslices between clients, we could expect to detect some
unfairness between clients (i.e. some windows not updating as fast as
others). This issue was noticed when inspecting a report of poor
interactivity resulting from excessively high __i915_spin_request usage.

Fixes regression from
commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 7 16:20:41 2015 +0100

     drm/i915: Optimistically spin for the request completion

v2: Try to assess the impact of the bug

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc; "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Eero Tamminen <eero.t.tamminen@intel.com>
Cc: "Rantala, Valtteri" <valtteri.rantala@intel.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/i915/i915_gem.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 8e2acdebc74a..7e1246410afc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1146,7 +1146,7 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
 	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
 }
 
-static int __i915_spin_request(struct drm_i915_gem_request *req)
+static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 {
 	unsigned long timeout;
 
@@ -1158,6 +1158,9 @@ static int __i915_spin_request(struct drm_i915_gem_request *req)
 		if (i915_gem_request_completed(req, true))
 			return 0;
 
+		if (signal_pending_state(state, current))
+			break;
+
 		if (time_after_eq(jiffies, timeout))
 			break;
 
@@ -1197,6 +1200,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	const bool irq_test_in_progress =
 		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
+	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
 	DEFINE_WAIT(wait);
 	unsigned long timeout_expire;
 	s64 before, now;
@@ -1229,7 +1233,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	before = ktime_get_raw_ns();
 
 	/* Optimistic spin for the next jiffie before touching IRQs */
-	ret = __i915_spin_request(req);
+	ret = __i915_spin_request(req, state);
 	if (ret == 0)
 		goto out;
 
@@ -1241,8 +1245,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	for (;;) {
 		struct timer_list timer;
 
-		prepare_to_wait(&ring->irq_queue, &wait,
-				interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE);
+		prepare_to_wait(&ring->irq_queue, &wait, state);
 
 		/* We need to check whether any gpu reset happened in between
 		 * the caller grabbing the seqno and now ... */
@@ -1260,7 +1263,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			break;
 		}
 
-		if (interruptible && signal_pending(current)) {
+		if (signal_pending_state(state, current)) {
 			ret = -ERESTARTSYS;
 			break;
 		}
-- 
2.6.3

[PATCH 02/32] drm/i915: Limit the busy wait on requests to 5us not 10ms!

[Chris Wilson]

When waiting for high frequency requests, the finite amount of time
required to set up the irq and wait upon it limits the response rate. By
busywaiting on the request completion for a short while we can service
the high frequency waits as quick as possible. However, if it is a slow
request, we want to sleep as quickly as possible. The tradeoff between
waiting and sleeping is roughly the time it takes to sleep on a request,
on the order of a microsecond. Based on measurements of synchronous
workloads from across big core and little atom, I have set the limit for
busywaiting as 10 microseconds. In most of the synchronous cases, we can
reduce the limit down to as little as 2 miscroseconds, but that leaves
quite a few test cases regressing by factors of 3 and more.

The code currently uses the jiffie clock, but that is far too coarse (on
the order of 10 milliseconds) and results in poor interactivity as the
CPU ends up being hogged by slow requests. To get microsecond resolution
we need to use a high resolution timer. The cheapest of which is polling
local_clock(), but that is only valid on the same CPU. If we switch CPUs
because the task was preempted, we can also use that as an indicator that
 the system is too busy to waste cycles on spinning and we should sleep
instead.

__i915_spin_request was introduced in
commit 2def4ad99befa25775dd2f714fdd4d92faec6e34 [v4.2]
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 7 16:20:41 2015 +0100

     drm/i915: Optimistically spin for the request completion

v2: Drop full u64 for unsigned long - the timer is 32bit wraparound safe,
so we can use native register sizes on smaller architectures. Mention
the approximate microseconds units for elapsed time and add some extra
comments describing the reason for busywaiting.

v3: Raise the limit to 10us
v4: Now 5us.

Reported-by: Jens Axboe <axboe@kernel.dk>
Link: https://lkml.org/lkml/2015/11/12/621
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Eero Tamminen <eero.t.tamminen@intel.com>
Cc: "Rantala, Valtteri" <valtteri.rantala@intel.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/i915/i915_gem.c | 47 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 7e1246410afc..46a84c447d8f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1146,14 +1146,57 @@ static bool missed_irq(struct drm_i915_private *dev_priv,
 	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
 }
 
+static unsigned long local_clock_us(unsigned *cpu)
+{
+	unsigned long t;
+
+	/* Cheaply and approximately convert from nanoseconds to microseconds.
+	 * The result and subsequent calculations are also defined in the same
+	 * approximate microseconds units. The principal source of timing
+	 * error here is from the simple truncation.
+	 *
+	 * Note that local_clock() is only defined wrt to the current CPU;
+	 * the comparisons are no longer valid if we switch CPUs. Instead of
+	 * blocking preemption for the entire busywait, we can detect the CPU
+	 * switch and use that as indicator of system load and a reason to
+	 * stop busywaiting, see busywait_stop().
+	 */
+	*cpu = get_cpu();
+	t = local_clock() >> 10;
+	put_cpu();
+
+	return t;
+}
+
+static bool busywait_stop(unsigned long timeout, unsigned cpu)
+{
+	unsigned this_cpu;
+
+	if (time_after(local_clock_us(&this_cpu), timeout))
+		return true;
+
+	return this_cpu != cpu;
+}
+
 static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 {
 	unsigned long timeout;
+	unsigned cpu;
+
+	/* When waiting for high frequency requests, e.g. during synchronous
+	 * rendering split between the CPU and GPU, the finite amount of time
+	 * required to set up the irq and wait upon it limits the response
+	 * rate. By busywaiting on the request completion for a short while we
+	 * can service the high frequency waits as quick as possible. However,
+	 * if it is a slow request, we want to sleep as quickly as possible.
+	 * The tradeoff between waiting and sleeping is roughly the time it
+	 * takes to sleep on a request, on the order of a microsecond.
+	 */
 
 	if (i915_gem_request_get_ring(req)->irq_refcount)
 		return -EBUSY;
 
-	timeout = jiffies + 1;
+	timeout = local_clock_us(&cpu) + 5;
 	while (!need_resched()) {
 		if (i915_gem_request_completed(req, true))
 			return 0;
@@ -1161,7 +1204,7 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 		if (signal_pending_state(state, current))
 			break;
 
-		if (time_after_eq(jiffies, timeout))
+		if (busywait_stop(timeout, cpu))
 			break;
 
 		cpu_relax_lowlatency();
-- 
2.6.3

[PATCH 03/32] drm/i915: Only spin whilst waiting on the current request

[Chris Wilson]

Limit busywaiting only to the request currently being processed by the
GPU. If the request is not currently being processed by the GPU, there
is a very low likelihood of it being completed within the 2 microsecond
spin timeout and so we will just be wasting CPU cycles.

v2: Check for logical inversion when rebasing - we were incorrectly
checking for this request being active, and instead busywaiting for
when the GPU was not yet processing the request of interest.

v3: Try another colour for the seqno names.
v4: Another colour for the function names.

v5: Remove the forced coherency when checking for the active request. On
reflection and plenty of recent experimentation, the issue is not a
cache coherency problem - but an irq/seqno ordering problem (timing issue).
Here, we do not need the w/a to force ordering of the read with an
interrupt.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Eero Tamminen <eero.t.tamminen@intel.com>
Cc: "Rantala, Valtteri" <valtteri.rantala@intel.com>
Cc: stable@vger.kernel.org
---
 drivers/gpu/drm/i915/i915_drv.h | 27 +++++++++++++++++++--------
 drivers/gpu/drm/i915/i915_gem.c |  8 +++++++-
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 5edd39352e97..8c4303b664d9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2182,8 +2182,17 @@ struct drm_i915_gem_request {
 	struct drm_i915_private *i915;
 	struct intel_engine_cs *ring;
 
-	/** GEM sequence number associated with this request. */
-	uint32_t seqno;
+	 /** GEM sequence number associated with the previous request,
+	  * when the HWS breadcrumb is equal to this the GPU is processing
+	  * this request.
+	  */
+	u32 previous_seqno;
+
+	 /** GEM sequence number associated with this request,
+	  * when the HWS breadcrumb is equal or greater than this the GPU
+	  * has finished processing this request.
+	  */
+	u32 seqno;
 
 	/** Position in the ringbuffer of the start of the request */
 	u32 head;
@@ -2958,15 +2967,17 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
 	return (int32_t)(seq1 - seq2) >= 0;
 }
 
+static inline bool i915_gem_request_started(struct drm_i915_gem_request *req,
+					   bool lazy_coherency)
+{
+	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
+	return i915_seqno_passed(seqno, req->previous_seqno);
+}
+
 static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
 					      bool lazy_coherency)
 {
-	u32 seqno;
-
-	BUG_ON(req == NULL);
-
-	seqno = req->ring->get_seqno(req->ring, lazy_coherency);
-
+	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
 	return i915_seqno_passed(seqno, req->seqno);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 46a84c447d8f..29d98ddbbc80 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1193,9 +1193,13 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 	 * takes to sleep on a request, on the order of a microsecond.
 	 */
 
-	if (i915_gem_request_get_ring(req)->irq_refcount)
+	if (req->ring->irq_refcount)
 		return -EBUSY;
 
+	/* Only spin if we know the GPU is processing this request */
+	if (!i915_gem_request_started(req, true))
+		return -EAGAIN;
+
 	timeout = local_clock_us(&cpu) + 5;
 	while (!need_resched()) {
 		if (i915_gem_request_completed(req, true))
@@ -1209,6 +1213,7 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 
 		cpu_relax_lowlatency();
 	}
+
 	if (i915_gem_request_completed(req, false))
 		return 0;
 
@@ -2600,6 +2605,7 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 	request->batch_obj = obj;
 
 	request->emitted_jiffies = jiffies;
+	request->previous_seqno = ring->last_submitted_seqno;
 	ring->last_submitted_seqno = request->seqno;
 	list_add_tail(&request->list, &ring->request_list);
 
-- 
2.6.3

Re: [PATCH 03/32] drm/i915: Only spin whilst waiting on the current request

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:32:59AM +0000, Chris Wilson wrote:
> Limit busywaiting only to the request currently being processed by the
> GPU. If the request is not currently being processed by the GPU, there
> is a very low likelihood of it being completed within the 2 microsecond
> spin timeout and so we will just be wasting CPU cycles.
> 
> v2: Check for logical inversion when rebasing - we were incorrectly
> checking for this request being active, and instead busywaiting for
> when the GPU was not yet processing the request of interest.
> 
> v3: Try another colour for the seqno names.
> v4: Another colour for the function names.
> 
> v5: Remove the forced coherency when checking for the active request. On
> reflection and plenty of recent experimentation, the issue is not a
> cache coherency problem - but an irq/seqno ordering problem (timing issue).
> Here, we do not need the w/a to force ordering of the read with an
> interrupt.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Eero Tamminen <eero.t.tamminen@intel.com>
> Cc: "Rantala, Valtteri" <valtteri.rantala@intel.com>
> Cc: stable@vger.kernel.org

Merged these 3 patches, thanks.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_drv.h | 27 +++++++++++++++++++--------
>  drivers/gpu/drm/i915/i915_gem.c |  8 +++++++-
>  2 files changed, 26 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 5edd39352e97..8c4303b664d9 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2182,8 +2182,17 @@ struct drm_i915_gem_request {
>  	struct drm_i915_private *i915;
>  	struct intel_engine_cs *ring;
>  
> -	/** GEM sequence number associated with this request. */
> -	uint32_t seqno;
> +	 /** GEM sequence number associated with the previous request,
> +	  * when the HWS breadcrumb is equal to this the GPU is processing
> +	  * this request.
> +	  */
> +	u32 previous_seqno;
> +
> +	 /** GEM sequence number associated with this request,
> +	  * when the HWS breadcrumb is equal or greater than this the GPU
> +	  * has finished processing this request.
> +	  */
> +	u32 seqno;
>  
>  	/** Position in the ringbuffer of the start of the request */
>  	u32 head;
> @@ -2958,15 +2967,17 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
>  	return (int32_t)(seq1 - seq2) >= 0;
>  }
>  
> +static inline bool i915_gem_request_started(struct drm_i915_gem_request *req,
> +					   bool lazy_coherency)
> +{
> +	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
> +	return i915_seqno_passed(seqno, req->previous_seqno);
> +}
> +
>  static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
>  					      bool lazy_coherency)
>  {
> -	u32 seqno;
> -
> -	BUG_ON(req == NULL);
> -
> -	seqno = req->ring->get_seqno(req->ring, lazy_coherency);
> -
> +	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
>  	return i915_seqno_passed(seqno, req->seqno);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 46a84c447d8f..29d98ddbbc80 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1193,9 +1193,13 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>  	 * takes to sleep on a request, on the order of a microsecond.
>  	 */
>  
> -	if (i915_gem_request_get_ring(req)->irq_refcount)
> +	if (req->ring->irq_refcount)
>  		return -EBUSY;
>  
> +	/* Only spin if we know the GPU is processing this request */
> +	if (!i915_gem_request_started(req, true))
> +		return -EAGAIN;
> +
>  	timeout = local_clock_us(&cpu) + 5;
>  	while (!need_resched()) {
>  		if (i915_gem_request_completed(req, true))
> @@ -1209,6 +1213,7 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>  
>  		cpu_relax_lowlatency();
>  	}
> +
>  	if (i915_gem_request_completed(req, false))
>  		return 0;
>  
> @@ -2600,6 +2605,7 @@ void __i915_add_request(struct drm_i915_gem_request *request,
>  	request->batch_obj = obj;
>  
>  	request->emitted_jiffies = jiffies;
> +	request->previous_seqno = ring->last_submitted_seqno;
>  	ring->last_submitted_seqno = request->seqno;
>  	list_add_tail(&request->list, &ring->request_list);
>  
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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[PATCH 04/32] drm/i915: Hide the atomic_read(reset_counter) behind a helper

[Chris Wilson]

This is principally a little bit of syntatic sugar to hide the
atomic_read()s throughout the code to retrieve the current reset_counter.
It also provides the other utility functions to check the reset state on the
already read reset_counter, so that (in later patches) we can read it once
and do multiple tests rather than risk the value changing between tests.

v2: Be strictly on converting existing i915_reset_in_progress() over to
the more verbose i915_reset_in_progress_or_wedged().

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_debugfs.c     |  4 ++--
 drivers/gpu/drm/i915/i915_drv.h         | 32 ++++++++++++++++++++++++++++----
 drivers/gpu/drm/i915/i915_gem.c         | 16 ++++++++--------
 drivers/gpu/drm/i915/i915_irq.c         |  2 +-
 drivers/gpu/drm/i915/intel_display.c    | 18 +++++++++++-------
 drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c |  4 ++--
 7 files changed, 53 insertions(+), 25 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 24318b79bcfc..c26a4c087f49 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4672,7 +4672,7 @@ i915_wedged_get(void *data, u64 *val)
 	struct drm_device *dev = data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
-	*val = atomic_read(&dev_priv->gpu_error.reset_counter);
+	*val = i915_reset_counter(&dev_priv->gpu_error);
 
 	return 0;
 }
@@ -4691,7 +4691,7 @@ i915_wedged_set(void *data, u64 val)
 	 * while it is writing to 'i915_wedged'
 	 */
 
-	if (i915_reset_in_progress(&dev_priv->gpu_error))
+	if (i915_reset_in_progress_or_wedged(&dev_priv->gpu_error))
 		return -EAGAIN;
 
 	intel_runtime_pm_get(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 8c4303b664d9..466caa0bc043 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2992,20 +2992,44 @@ void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
 int __must_check i915_gem_check_wedge(struct i915_gpu_error *error,
 				      bool interruptible);
 
+static inline u32 i915_reset_counter(struct i915_gpu_error *error)
+{
+	return atomic_read(&error->reset_counter);
+}
+
+static inline bool __i915_reset_in_progress(u32 reset)
+{
+	return unlikely(reset & I915_RESET_IN_PROGRESS_FLAG);
+}
+
+static inline bool __i915_reset_in_progress_or_wedged(u32 reset)
+{
+	return unlikely(reset & (I915_RESET_IN_PROGRESS_FLAG | I915_WEDGED));
+}
+
+static inline bool __i915_terminally_wedged(u32 reset)
+{
+	return unlikely(reset & I915_WEDGED);
+}
+
 static inline bool i915_reset_in_progress(struct i915_gpu_error *error)
 {
-	return unlikely(atomic_read(&error->reset_counter)
-			& (I915_RESET_IN_PROGRESS_FLAG | I915_WEDGED));
+	return __i915_reset_in_progress(i915_reset_counter(error));
+}
+
+static inline bool i915_reset_in_progress_or_wedged(struct i915_gpu_error *error)
+{
+	return __i915_reset_in_progress_or_wedged(i915_reset_counter(error));
 }
 
 static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
 {
-	return atomic_read(&error->reset_counter) & I915_WEDGED;
+	return __i915_terminally_wedged(i915_reset_counter(error));
 }
 
 static inline u32 i915_reset_count(struct i915_gpu_error *error)
 {
-	return ((atomic_read(&error->reset_counter) & ~I915_WEDGED) + 1) / 2;
+	return ((i915_reset_counter(error) & ~I915_WEDGED) + 1) / 2;
 }
 
 static inline bool i915_stop_ring_allow_ban(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 29d98ddbbc80..0b3e0534baa3 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -85,7 +85,7 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
 {
 	int ret;
 
-#define EXIT_COND (!i915_reset_in_progress(error) || \
+#define EXIT_COND (!i915_reset_in_progress_or_wedged(error) || \
 		   i915_terminally_wedged(error))
 	if (EXIT_COND)
 		return 0;
@@ -1113,7 +1113,7 @@ int
 i915_gem_check_wedge(struct i915_gpu_error *error,
 		     bool interruptible)
 {
-	if (i915_reset_in_progress(error)) {
+	if (i915_reset_in_progress_or_wedged(error)) {
 		/* Non-interruptible callers can't handle -EAGAIN, hence return
 		 * -EIO unconditionally for these. */
 		if (!interruptible)
@@ -1297,7 +1297,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 
 		/* We need to check whether any gpu reset happened in between
 		 * the caller grabbing the seqno and now ... */
-		if (reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter)) {
+		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
 			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
 			 * is truely gone. */
 			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
@@ -1475,7 +1475,7 @@ i915_wait_request(struct drm_i915_gem_request *req)
 		return ret;
 
 	ret = __i915_wait_request(req,
-				  atomic_read(&dev_priv->gpu_error.reset_counter),
+				  i915_reset_counter(&dev_priv->gpu_error),
 				  interruptible, NULL, NULL);
 	if (ret)
 		return ret;
@@ -1564,7 +1564,7 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
 	if (ret)
 		return ret;
 
-	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 
 	if (readonly) {
 		struct drm_i915_gem_request *req;
@@ -3114,7 +3114,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 	}
 
 	drm_gem_object_unreference(&obj->base);
-	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 
 	for (i = 0; i < I915_NUM_RINGS; i++) {
 		if (obj->last_read_req[i] == NULL)
@@ -3159,7 +3159,7 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
 	if (!i915_semaphore_is_enabled(obj->base.dev)) {
 		struct drm_i915_private *i915 = to_i915(obj->base.dev);
 		ret = __i915_wait_request(from_req,
-					  atomic_read(&i915->gpu_error.reset_counter),
+					  i915_reset_counter(&i915->gpu_error),
 					  i915->mm.interruptible,
 					  NULL,
 					  &i915->rps.semaphores);
@@ -4133,7 +4133,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 
 		target = request;
 	}
-	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 	if (target)
 		i915_gem_request_reference(target);
 	spin_unlock(&file_priv->mm.lock);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 86664d1b3389..60dff3f89531 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2452,7 +2452,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
 	 * the reset in-progress bit is only ever set by code outside of this
 	 * work we don't need to worry about any other races.
 	 */
-	if (i915_reset_in_progress(error) && !i915_terminally_wedged(error)) {
+	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
 		DRM_DEBUG_DRIVER("resetting chip\n");
 		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
 				   reset_event);
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 7dd7200d3ba9..cc47c0206294 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3285,10 +3285,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	unsigned reset_counter;
 	bool pending;
 
-	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
-	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
+	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
+	if (intel_crtc->reset_counter != reset_counter ||
+	    __i915_reset_in_progress_or_wedged(reset_counter))
 		return false;
 
 	spin_lock_irq(&dev->event_lock);
@@ -10942,9 +10944,11 @@ static bool page_flip_finished(struct intel_crtc *crtc)
 {
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
+	unsigned reset_counter;
 
-	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
-	    crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
+	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
+	if (crtc->reset_counter != reset_counter ||
+	    __i915_reset_in_progress_or_wedged(reset_counter))
 		return true;
 
 	/*
@@ -11601,7 +11605,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 		goto cleanup;
 
 	atomic_inc(&intel_crtc->unpin_work_count);
-	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 
 	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
 		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
@@ -13388,10 +13392,10 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 		return ret;
 
 	ret = drm_atomic_helper_prepare_planes(dev, state);
-	if (!ret && !async && !i915_reset_in_progress(&dev_priv->gpu_error)) {
+	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
 		u32 reset_counter;
 
-		reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
+		reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 		mutex_unlock(&dev->struct_mutex);
 
 		for_each_plane_in_state(state, plane, plane_state, i) {
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7644c48da4ea..86404b03dc91 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -983,7 +983,7 @@ void intel_logical_ring_stop(struct intel_engine_cs *ring)
 		return;
 
 	ret = intel_ring_idle(ring);
-	if (ret && !i915_reset_in_progress(&to_i915(ring->dev)->gpu_error))
+	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
 		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
 			  ring->name, ret);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index eefce9a3e9c8..d71fa77055f9 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2274,7 +2274,7 @@ int intel_ring_idle(struct intel_engine_cs *ring)
 
 	/* Make sure we do not trigger any retires */
 	return __i915_wait_request(req,
-				   atomic_read(&to_i915(ring->dev)->gpu_error.reset_counter),
+				   i915_reset_counter(&to_i915(ring->dev)->gpu_error),
 				   to_i915(ring->dev)->mm.interruptible,
 				   NULL, NULL);
 }
@@ -3068,7 +3068,7 @@ intel_stop_ring_buffer(struct intel_engine_cs *ring)
 		return;
 
 	ret = intel_ring_idle(ring);
-	if (ret && !i915_reset_in_progress(&to_i915(ring->dev)->gpu_error))
+	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
 		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
 			  ring->name, ret);
 
-- 
2.6.3

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 04/32] drm/i915: Hide the atomic_read(reset_counter) behind a helper

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:00AM +0000, Chris Wilson wrote:
> This is principally a little bit of syntatic sugar to hide the
> atomic_read()s throughout the code to retrieve the current reset_counter.
> It also provides the other utility functions to check the reset state on the
> already read reset_counter, so that (in later patches) we can read it once
> and do multiple tests rather than risk the value changing between tests.
> 
> v2: Be strictly on converting existing i915_reset_in_progress() over to
> the more verbose i915_reset_in_progress_or_wedged().
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/i915_debugfs.c     |  4 ++--
>  drivers/gpu/drm/i915/i915_drv.h         | 32 ++++++++++++++++++++++++++++----
>  drivers/gpu/drm/i915/i915_gem.c         | 16 ++++++++--------
>  drivers/gpu/drm/i915/i915_irq.c         |  2 +-
>  drivers/gpu/drm/i915/intel_display.c    | 18 +++++++++++-------
>  drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
>  drivers/gpu/drm/i915/intel_ringbuffer.c |  4 ++--
>  7 files changed, 53 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 24318b79bcfc..c26a4c087f49 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4672,7 +4672,7 @@ i915_wedged_get(void *data, u64 *val)
>  	struct drm_device *dev = data;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> -	*val = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	*val = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	return 0;
>  }
> @@ -4691,7 +4691,7 @@ i915_wedged_set(void *data, u64 val)
>  	 * while it is writing to 'i915_wedged'
>  	 */
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error))
> +	if (i915_reset_in_progress_or_wedged(&dev_priv->gpu_error))
>  		return -EAGAIN;
>  
>  	intel_runtime_pm_get(dev_priv);
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 8c4303b664d9..466caa0bc043 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2992,20 +2992,44 @@ void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
>  int __must_check i915_gem_check_wedge(struct i915_gpu_error *error,
>  				      bool interruptible);
>  
> +static inline u32 i915_reset_counter(struct i915_gpu_error *error)
> +{
> +	return atomic_read(&error->reset_counter);
> +}
> +
> +static inline bool __i915_reset_in_progress(u32 reset)
> +{
> +	return unlikely(reset & I915_RESET_IN_PROGRESS_FLAG);
> +}
> +
> +static inline bool __i915_reset_in_progress_or_wedged(u32 reset)
> +{
> +	return unlikely(reset & (I915_RESET_IN_PROGRESS_FLAG | I915_WEDGED));
> +}
> +
> +static inline bool __i915_terminally_wedged(u32 reset)
> +{
> +	return unlikely(reset & I915_WEDGED);
> +}
> +
>  static inline bool i915_reset_in_progress(struct i915_gpu_error *error)
>  {
> -	return unlikely(atomic_read(&error->reset_counter)
> -			& (I915_RESET_IN_PROGRESS_FLAG | I915_WEDGED));
> +	return __i915_reset_in_progress(i915_reset_counter(error));
> +}
> +
> +static inline bool i915_reset_in_progress_or_wedged(struct i915_gpu_error *error)
> +{
> +	return __i915_reset_in_progress_or_wedged(i915_reset_counter(error));
>  }
>  
>  static inline bool i915_terminally_wedged(struct i915_gpu_error *error)
>  {
> -	return atomic_read(&error->reset_counter) & I915_WEDGED;
> +	return __i915_terminally_wedged(i915_reset_counter(error));
>  }
>  
>  static inline u32 i915_reset_count(struct i915_gpu_error *error)
>  {
> -	return ((atomic_read(&error->reset_counter) & ~I915_WEDGED) + 1) / 2;
> +	return ((i915_reset_counter(error) & ~I915_WEDGED) + 1) / 2;
>  }
>  
>  static inline bool i915_stop_ring_allow_ban(struct drm_i915_private *dev_priv)
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 29d98ddbbc80..0b3e0534baa3 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -85,7 +85,7 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
>  {
>  	int ret;
>  
> -#define EXIT_COND (!i915_reset_in_progress(error) || \
> +#define EXIT_COND (!i915_reset_in_progress_or_wedged(error) || \
>  		   i915_terminally_wedged(error))
>  	if (EXIT_COND)
>  		return 0;
> @@ -1113,7 +1113,7 @@ int
>  i915_gem_check_wedge(struct i915_gpu_error *error,
>  		     bool interruptible)
>  {
> -	if (i915_reset_in_progress(error)) {
> +	if (i915_reset_in_progress_or_wedged(error)) {
>  		/* Non-interruptible callers can't handle -EAGAIN, hence return
>  		 * -EIO unconditionally for these. */
>  		if (!interruptible)
> @@ -1297,7 +1297,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  
>  		/* We need to check whether any gpu reset happened in between
>  		 * the caller grabbing the seqno and now ... */
> -		if (reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter)) {
> +		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
>  			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
>  			 * is truely gone. */
>  			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> @@ -1475,7 +1475,7 @@ i915_wait_request(struct drm_i915_gem_request *req)
>  		return ret;
>  
>  	ret = __i915_wait_request(req,
> -				  atomic_read(&dev_priv->gpu_error.reset_counter),
> +				  i915_reset_counter(&dev_priv->gpu_error),
>  				  interruptible, NULL, NULL);
>  	if (ret)
>  		return ret;
> @@ -1564,7 +1564,7 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
>  	if (ret)
>  		return ret;
>  
> -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	if (readonly) {
>  		struct drm_i915_gem_request *req;
> @@ -3114,7 +3114,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  	}
>  
>  	drm_gem_object_unreference(&obj->base);
> -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	for (i = 0; i < I915_NUM_RINGS; i++) {
>  		if (obj->last_read_req[i] == NULL)
> @@ -3159,7 +3159,7 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
>  	if (!i915_semaphore_is_enabled(obj->base.dev)) {
>  		struct drm_i915_private *i915 = to_i915(obj->base.dev);
>  		ret = __i915_wait_request(from_req,
> -					  atomic_read(&i915->gpu_error.reset_counter),
> +					  i915_reset_counter(&i915->gpu_error),
>  					  i915->mm.interruptible,
>  					  NULL,
>  					  &i915->rps.semaphores);
> @@ -4133,7 +4133,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  
>  		target = request;
>  	}
> -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  	if (target)
>  		i915_gem_request_reference(target);
>  	spin_unlock(&file_priv->mm.lock);
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 86664d1b3389..60dff3f89531 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2452,7 +2452,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
>  	 * the reset in-progress bit is only ever set by code outside of this
>  	 * work we don't need to worry about any other races.
>  	 */
> -	if (i915_reset_in_progress(error) && !i915_terminally_wedged(error)) {
> +	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
>  		DRM_DEBUG_DRIVER("resetting chip\n");
>  		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
>  				   reset_event);
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 7dd7200d3ba9..cc47c0206294 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3285,10 +3285,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
>  	struct drm_device *dev = crtc->dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> +	unsigned reset_counter;
>  	bool pending;
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> -	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> +	if (intel_crtc->reset_counter != reset_counter ||
> +	    __i915_reset_in_progress_or_wedged(reset_counter))
>  		return false;
>  
>  	spin_lock_irq(&dev->event_lock);
> @@ -10942,9 +10944,11 @@ static bool page_flip_finished(struct intel_crtc *crtc)
>  {
>  	struct drm_device *dev = crtc->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	unsigned reset_counter;
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> -	    crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> +	if (crtc->reset_counter != reset_counter ||
> +	    __i915_reset_in_progress_or_wedged(reset_counter))
>  		return true;
>  
>  	/*
> @@ -11601,7 +11605,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  		goto cleanup;
>  
>  	atomic_inc(&intel_crtc->unpin_work_count);
> -	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
>  		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
> @@ -13388,10 +13392,10 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  		return ret;
>  
>  	ret = drm_atomic_helper_prepare_planes(dev, state);
> -	if (!ret && !async && !i915_reset_in_progress(&dev_priv->gpu_error)) {
> +	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
>  		u32 reset_counter;
>  
> -		reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +		reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  		mutex_unlock(&dev->struct_mutex);
>  
>  		for_each_plane_in_state(state, plane, plane_state, i) {
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 7644c48da4ea..86404b03dc91 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -983,7 +983,7 @@ void intel_logical_ring_stop(struct intel_engine_cs *ring)
>  		return;
>  
>  	ret = intel_ring_idle(ring);
> -	if (ret && !i915_reset_in_progress(&to_i915(ring->dev)->gpu_error))
> +	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
>  		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
>  			  ring->name, ret);
>  
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index eefce9a3e9c8..d71fa77055f9 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2274,7 +2274,7 @@ int intel_ring_idle(struct intel_engine_cs *ring)
>  
>  	/* Make sure we do not trigger any retires */
>  	return __i915_wait_request(req,
> -				   atomic_read(&to_i915(ring->dev)->gpu_error.reset_counter),
> +				   i915_reset_counter(&to_i915(ring->dev)->gpu_error),
>  				   to_i915(ring->dev)->mm.interruptible,
>  				   NULL, NULL);
>  }
> @@ -3068,7 +3068,7 @@ intel_stop_ring_buffer(struct intel_engine_cs *ring)
>  		return;
>  
>  	ret = intel_ring_idle(ring);
> -	if (ret && !i915_reset_in_progress(&to_i915(ring->dev)->gpu_error))
> +	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
>  		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
>  			  ring->name, ret);
>  
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH 04/32] drm/i915: Hide the atomic_read(reset_counter) behind a helper

[Daniel Vetter]

Hit send too early ;-)

On Fri, Dec 11, 2015 at 11:33:00AM +0000, Chris Wilson wrote:
> @@ -4133,7 +4133,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  
>  		target = request;
>  	}
> -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  	if (target)
>  		i915_gem_request_reference(target);
>  	spin_unlock(&file_priv->mm.lock);
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 86664d1b3389..60dff3f89531 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2452,7 +2452,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
>  	 * the reset in-progress bit is only ever set by code outside of this
>  	 * work we don't need to worry about any other races.
>  	 */
> -	if (i915_reset_in_progress(error) && !i915_terminally_wedged(error)) {
> +	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {

Well maybe simplify this one here.

>  		DRM_DEBUG_DRIVER("resetting chip\n");
>  		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
>  				   reset_event);
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 7dd7200d3ba9..cc47c0206294 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3285,10 +3285,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
>  	struct drm_device *dev = crtc->dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> +	unsigned reset_counter;
>  	bool pending;
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> -	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> +	if (intel_crtc->reset_counter != reset_counter ||
> +	    __i915_reset_in_progress_or_wedged(reset_counter))
>  		return false;
>  
>  	spin_lock_irq(&dev->event_lock);
> @@ -10942,9 +10944,11 @@ static bool page_flip_finished(struct intel_crtc *crtc)
>  {
>  	struct drm_device *dev = crtc->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	unsigned reset_counter;
>  
> -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> -	    crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> +	if (crtc->reset_counter != reset_counter ||
> +	    __i915_reset_in_progress_or_wedged(reset_counter))
>  		return true;
>  
>  	/*
> @@ -11601,7 +11605,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  		goto cleanup;
>  
>  	atomic_inc(&intel_crtc->unpin_work_count);
> -	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> +	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
>  		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
> @@ -13388,10 +13392,10 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  		return ret;
>  
>  	ret = drm_atomic_helper_prepare_planes(dev, state);
> -	if (!ret && !async && !i915_reset_in_progress(&dev_priv->gpu_error)) {
> +	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {

I guess we should also drop the _or_wedged here since dead gpu isn't a
problem for the modeset code? Or is that later on in the series ...
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH 04/32] drm/i915: Hide the atomic_read(reset_counter) behind a helper

[Daniel Vetter]

On Wed, Dec 16, 2015 at 10:33:32AM +0100, Daniel Vetter wrote:
> Hit send too early ;-)
> 
> On Fri, Dec 11, 2015 at 11:33:00AM +0000, Chris Wilson wrote:
> > @@ -4133,7 +4133,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
> >  
> >  		target = request;
> >  	}
> > -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> >  	if (target)
> >  		i915_gem_request_reference(target);
> >  	spin_unlock(&file_priv->mm.lock);
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index 86664d1b3389..60dff3f89531 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -2452,7 +2452,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
> >  	 * the reset in-progress bit is only ever set by code outside of this
> >  	 * work we don't need to worry about any other races.
> >  	 */
> > -	if (i915_reset_in_progress(error) && !i915_terminally_wedged(error)) {
> > +	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
> 
> Well maybe simplify this one here.

And since I seem to be making a mess of this thread: r-b stands without or
with this.
-Daniel

> 
> >  		DRM_DEBUG_DRIVER("resetting chip\n");
> >  		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
> >  				   reset_event);
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 7dd7200d3ba9..cc47c0206294 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -3285,10 +3285,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
> >  	struct drm_device *dev = crtc->dev;
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> > +	unsigned reset_counter;
> >  	bool pending;
> >  
> > -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> > -	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> > +	if (intel_crtc->reset_counter != reset_counter ||
> > +	    __i915_reset_in_progress_or_wedged(reset_counter))
> >  		return false;
> >  
> >  	spin_lock_irq(&dev->event_lock);
> > @@ -10942,9 +10944,11 @@ static bool page_flip_finished(struct intel_crtc *crtc)
> >  {
> >  	struct drm_device *dev = crtc->base.dev;
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > +	unsigned reset_counter;
> >  
> > -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> > -	    crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> > +	if (crtc->reset_counter != reset_counter ||
> > +	    __i915_reset_in_progress_or_wedged(reset_counter))
> >  		return true;
> >  
> >  	/*
> > @@ -11601,7 +11605,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
> >  		goto cleanup;
> >  
> >  	atomic_inc(&intel_crtc->unpin_work_count);
> > -	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> > +	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> >  
> >  	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
> >  		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
> > @@ -13388,10 +13392,10 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
> >  		return ret;
> >  
> >  	ret = drm_atomic_helper_prepare_planes(dev, state);
> > -	if (!ret && !async && !i915_reset_in_progress(&dev_priv->gpu_error)) {
> > +	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
> 
> I guess we should also drop the _or_wedged here since dead gpu isn't a
> problem for the modeset code? Or is that later on in the series ...
> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
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Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 04/32] drm/i915: Hide the atomic_read(reset_counter) behind a helper

[Chris Wilson]

On Wed, Dec 16, 2015 at 10:33:32AM +0100, Daniel Vetter wrote:
> Hit send too early ;-)
> 
> On Fri, Dec 11, 2015 at 11:33:00AM +0000, Chris Wilson wrote:
> > @@ -4133,7 +4133,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
> >  
> >  		target = request;
> >  	}
> > -	reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> >  	if (target)
> >  		i915_gem_request_reference(target);
> >  	spin_unlock(&file_priv->mm.lock);
> > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > index 86664d1b3389..60dff3f89531 100644
> > --- a/drivers/gpu/drm/i915/i915_irq.c
> > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > @@ -2452,7 +2452,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
> >  	 * the reset in-progress bit is only ever set by code outside of this
> >  	 * work we don't need to worry about any other races.
> >  	 */
> > -	if (i915_reset_in_progress(error) && !i915_terminally_wedged(error)) {
> > +	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
> 
> Well maybe simplify this one here.
> 
> >  		DRM_DEBUG_DRIVER("resetting chip\n");
> >  		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
> >  				   reset_event);
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index 7dd7200d3ba9..cc47c0206294 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -3285,10 +3285,12 @@ static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
> >  	struct drm_device *dev = crtc->dev;
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> >  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
> > +	unsigned reset_counter;
> >  	bool pending;
> >  
> > -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> > -	    intel_crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> > +	if (intel_crtc->reset_counter != reset_counter ||
> > +	    __i915_reset_in_progress_or_wedged(reset_counter))
> >  		return false;
> >  
> >  	spin_lock_irq(&dev->event_lock);
> > @@ -10942,9 +10944,11 @@ static bool page_flip_finished(struct intel_crtc *crtc)
> >  {
> >  	struct drm_device *dev = crtc->base.dev;
> >  	struct drm_i915_private *dev_priv = dev->dev_private;
> > +	unsigned reset_counter;
> >  
> > -	if (i915_reset_in_progress(&dev_priv->gpu_error) ||
> > -	    crtc->reset_counter != atomic_read(&dev_priv->gpu_error.reset_counter))
> > +	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> > +	if (crtc->reset_counter != reset_counter ||
> > +	    __i915_reset_in_progress_or_wedged(reset_counter))
> >  		return true;
> >  
> >  	/*
> > @@ -11601,7 +11605,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
> >  		goto cleanup;
> >  
> >  	atomic_inc(&intel_crtc->unpin_work_count);
> > -	intel_crtc->reset_counter = atomic_read(&dev_priv->gpu_error.reset_counter);
> > +	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> >  
> >  	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
> >  		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
> > @@ -13388,10 +13392,10 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
> >  		return ret;
> >  
> >  	ret = drm_atomic_helper_prepare_planes(dev, state);
> > -	if (!ret && !async && !i915_reset_in_progress(&dev_priv->gpu_error)) {
> > +	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
> 
> I guess we should also drop the _or_wedged here since dead gpu isn't a
> problem for the modeset code? Or is that later on in the series ...

Both of these turn up later in the series. My goal in this patch was to
try a mechinical translation (albeit to a more verbose name). It was
only when I was sure that we had the nuances of the reset handler under
control that I felt safe in making changes to the tests.

So I'm going to take your r-b and run with it!
-Chris

-- 
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[PATCH 05/32] drm/i915: Simplify checking of GPU reset_counter in display pageflips

[Chris Wilson]

If we, when we store the reset_counter for the operation, we ensure that
it is not in a wedged or in the middle of a reset, we can then assert that
if any reset occurs the reset_counter must change. Later we can just
compare the operation's reset epoch against the current counter to see
if we need to abort the operation (to handle the hang).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index cc47c0206294..8b6028cd619f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3283,14 +3283,12 @@ void intel_finish_reset(struct drm_device *dev)
 static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	unsigned reset_counter;
 	bool pending;
 
-	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-	if (intel_crtc->reset_counter != reset_counter ||
-	    __i915_reset_in_progress_or_wedged(reset_counter))
+	reset_counter = i915_reset_counter(&to_i915(dev)->gpu_error);
+	if (intel_crtc->reset_counter != reset_counter)
 		return false;
 
 	spin_lock_irq(&dev->event_lock);
@@ -10947,8 +10945,7 @@ static bool page_flip_finished(struct intel_crtc *crtc)
 	unsigned reset_counter;
 
 	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-	if (crtc->reset_counter != reset_counter ||
-	    __i915_reset_in_progress_or_wedged(reset_counter))
+	if (crtc->reset_counter != reset_counter)
 		return true;
 
 	/*
@@ -11604,8 +11601,13 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	if (ret)
 		goto cleanup;
 
-	atomic_inc(&intel_crtc->unpin_work_count);
 	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
+	if (__i915_reset_in_progress_or_wedged(intel_crtc->reset_counter)) {
+		ret = -EIO;
+		goto cleanup;
+	}
+
+	atomic_inc(&intel_crtc->unpin_work_count);
 
 	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
 		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
-- 
2.6.3

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Re: [PATCH 05/32] drm/i915: Simplify checking of GPU reset_counter in display pageflips

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:01AM +0000, Chris Wilson wrote:
> If we, when we store the reset_counter for the operation, we ensure that
> it is not in a wedged or in the middle of a reset, we can then assert that
> if any reset occurs the reset_counter must change. Later we can just
> compare the operation's reset epoch against the current counter to see
> if we need to abort the operation (to handle the hang).
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/intel_display.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index cc47c0206294..8b6028cd619f 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -3283,14 +3283,12 @@ void intel_finish_reset(struct drm_device *dev)
>  static bool intel_crtc_has_pending_flip(struct drm_crtc *crtc)
>  {
>  	struct drm_device *dev = crtc->dev;
> -	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>  	unsigned reset_counter;
>  	bool pending;
>  
> -	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> -	if (intel_crtc->reset_counter != reset_counter ||
> -	    __i915_reset_in_progress_or_wedged(reset_counter))
> +	reset_counter = i915_reset_counter(&to_i915(dev)->gpu_error);
> +	if (intel_crtc->reset_counter != reset_counter)
>  		return false;
>  
>  	spin_lock_irq(&dev->event_lock);
> @@ -10947,8 +10945,7 @@ static bool page_flip_finished(struct intel_crtc *crtc)
>  	unsigned reset_counter;
>  
>  	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> -	if (crtc->reset_counter != reset_counter ||
> -	    __i915_reset_in_progress_or_wedged(reset_counter))
> +	if (crtc->reset_counter != reset_counter)
>  		return true;
>  
>  	/*
> @@ -11604,8 +11601,13 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
>  	if (ret)
>  		goto cleanup;
>  
> -	atomic_inc(&intel_crtc->unpin_work_count);
>  	intel_crtc->reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> +	if (__i915_reset_in_progress_or_wedged(intel_crtc->reset_counter)) {
> +		ret = -EIO;
> +		goto cleanup;
> +	}
> +
> +	atomic_inc(&intel_crtc->unpin_work_count);
>  
>  	if (INTEL_INFO(dev)->gen >= 5 || IS_G4X(dev))
>  		work->flip_count = I915_READ(PIPE_FLIPCOUNT_G4X(pipe)) + 1;
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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[PATCH 06/32] drm/i915: Tighten reset_counter for reset status

[Chris Wilson]

In the reset_counter, we use two bits to track a GPU hang and reset. The
low bit is a "reset-in-progress" flag that we set to signal when we need
to break waiters in order for the recovery task to grab the mutex. As
soon as the recovery task has the mutex, we can clear that flag (which
we do by incrementing the reset_counter thereby incrementing the gobal
reset epoch). By clearing that flag when the recovery task holds the
struct_mutex, we can forgo a second flag that simply tells GEM to ignore
the "reset-in-progress" flag.

The second flag we store in the reset_counter is whether the
reset failed and we consider the GPU terminally wedged. Whilst this flag
is set, all access to the GPU (at least through GEM rather than direct mmio
access) is verboten.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_debugfs.c |  4 ++--
 drivers/gpu/drm/i915/i915_drv.c     | 39 ++++++++++++++++++++++---------------
 drivers/gpu/drm/i915/i915_drv.h     |  3 ---
 drivers/gpu/drm/i915/i915_gem.c     | 27 +++++++++----------------
 drivers/gpu/drm/i915/i915_irq.c     | 21 ++------------------
 5 files changed, 36 insertions(+), 58 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index c26a4c087f49..d5f66bbdb160 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4672,7 +4672,7 @@ i915_wedged_get(void *data, u64 *val)
 	struct drm_device *dev = data;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 
-	*val = i915_reset_counter(&dev_priv->gpu_error);
+	*val = i915_terminally_wedged(&dev_priv->gpu_error);
 
 	return 0;
 }
@@ -4691,7 +4691,7 @@ i915_wedged_set(void *data, u64 val)
 	 * while it is writing to 'i915_wedged'
 	 */
 
-	if (i915_reset_in_progress_or_wedged(&dev_priv->gpu_error))
+	if (i915_reset_in_progress(&dev_priv->gpu_error))
 		return -EAGAIN;
 
 	intel_runtime_pm_get(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 8ddfcce92cf1..8bdc51bc00a4 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -858,23 +858,32 @@ int i915_resume_switcheroo(struct drm_device *dev)
 int i915_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	bool simulated;
+	struct i915_gpu_error *error = &dev_priv->gpu_error;
+	unsigned reset_counter;
 	int ret;
 
 	intel_reset_gt_powersave(dev);
 
 	mutex_lock(&dev->struct_mutex);
 
-	i915_gem_reset(dev);
+	/* Clear any previous failed attempts at recovery. Time to try again. */
+	atomic_andnot(I915_WEDGED, &error->reset_counter);
 
-	simulated = dev_priv->gpu_error.stop_rings != 0;
+	/* Clear the reset-in-progress flag and increment the reset epoch. */
+	reset_counter = atomic_inc_return(&error->reset_counter);
+	if (WARN_ON(__i915_reset_in_progress(reset_counter))) {
+		ret = -EIO;
+		goto error;
+	}
+
+	i915_gem_reset(dev);
 
 	ret = intel_gpu_reset(dev);
 
 	/* Also reset the gpu hangman. */
-	if (simulated) {
+	if (error->stop_rings != 0) {
 		DRM_INFO("Simulated gpu hang, resetting stop_rings\n");
-		dev_priv->gpu_error.stop_rings = 0;
+		error->stop_rings = 0;
 		if (ret == -ENODEV) {
 			DRM_INFO("Reset not implemented, but ignoring "
 				 "error for simulated gpu hangs\n");
@@ -887,8 +896,7 @@ int i915_reset(struct drm_device *dev)
 
 	if (ret) {
 		DRM_ERROR("Failed to reset chip: %i\n", ret);
-		mutex_unlock(&dev->struct_mutex);
-		return ret;
+		goto error;
 	}
 
 	intel_overlay_reset(dev_priv);
@@ -907,20 +915,14 @@ int i915_reset(struct drm_device *dev)
 	 * was running at the time of the reset (i.e. we weren't VT
 	 * switched away).
 	 */
-
-	/* Used to prevent gem_check_wedged returning -EAGAIN during gpu reset */
-	dev_priv->gpu_error.reload_in_reset = true;
-
 	ret = i915_gem_init_hw(dev);
-
-	dev_priv->gpu_error.reload_in_reset = false;
-
-	mutex_unlock(&dev->struct_mutex);
 	if (ret) {
 		DRM_ERROR("Failed hw init on reset %d\n", ret);
-		return ret;
+		goto error;
 	}
 
+	mutex_unlock(&dev->struct_mutex);
+
 	/*
 	 * rps/rc6 re-init is necessary to restore state lost after the
 	 * reset and the re-install of gt irqs. Skip for ironlake per
@@ -931,6 +933,11 @@ int i915_reset(struct drm_device *dev)
 		intel_enable_gt_powersave(dev);
 
 	return 0;
+
+error:
+	atomic_or(I915_WEDGED, &error->reset_counter);
+	mutex_unlock(&dev->struct_mutex);
+	return ret;
 }
 
 static int i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 466caa0bc043..1043ddd670a5 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1384,9 +1384,6 @@ struct i915_gpu_error {
 
 	/* For missed irq/seqno simulation. */
 	unsigned int test_irq_rings;
-
-	/* Used to prevent gem_check_wedged returning -EAGAIN during gpu reset   */
-	bool reload_in_reset;
 };
 
 enum modeset_restore {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 0b3e0534baa3..27e617b76418 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -85,9 +85,7 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
 {
 	int ret;
 
-#define EXIT_COND (!i915_reset_in_progress_or_wedged(error) || \
-		   i915_terminally_wedged(error))
-	if (EXIT_COND)
+	if (!i915_reset_in_progress(error))
 		return 0;
 
 	/*
@@ -96,17 +94,16 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
 	 * we should simply try to bail out and fail as gracefully as possible.
 	 */
 	ret = wait_event_interruptible_timeout(error->reset_queue,
-					       EXIT_COND,
+					       !i915_reset_in_progress(error),
 					       10*HZ);
 	if (ret == 0) {
 		DRM_ERROR("Timed out waiting for the gpu reset to complete\n");
 		return -EIO;
 	} else if (ret < 0) {
 		return ret;
+	} else {
+		return 0;
 	}
-#undef EXIT_COND
-
-	return 0;
 }
 
 int i915_mutex_lock_interruptible(struct drm_device *dev)
@@ -1114,22 +1111,16 @@ i915_gem_check_wedge(struct i915_gpu_error *error,
 		     bool interruptible)
 {
 	if (i915_reset_in_progress_or_wedged(error)) {
+		/* Recovery complete, but the reset failed ... */
+		if (i915_terminally_wedged(error))
+			return -EIO;
+
 		/* Non-interruptible callers can't handle -EAGAIN, hence return
 		 * -EIO unconditionally for these. */
 		if (!interruptible)
 			return -EIO;
 
-		/* Recovery complete, but the reset failed ... */
-		if (i915_terminally_wedged(error))
-			return -EIO;
-
-		/*
-		 * Check if GPU Reset is in progress - we need intel_ring_begin
-		 * to work properly to reinit the hw state while the gpu is
-		 * still marked as reset-in-progress. Handle this with a flag.
-		 */
-		if (!error->reload_in_reset)
-			return -EAGAIN;
+		return -EAGAIN;
 	}
 
 	return 0;
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 60dff3f89531..88206c0404d7 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2434,7 +2434,6 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 static void i915_reset_and_wakeup(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
-	struct i915_gpu_error *error = &dev_priv->gpu_error;
 	char *error_event[] = { I915_ERROR_UEVENT "=1", NULL };
 	char *reset_event[] = { I915_RESET_UEVENT "=1", NULL };
 	char *reset_done_event[] = { I915_ERROR_UEVENT "=0", NULL };
@@ -2452,7 +2451,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
 	 * the reset in-progress bit is only ever set by code outside of this
 	 * work we don't need to worry about any other races.
 	 */
-	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
+	if (i915_reset_in_progress(&dev_priv->gpu_error)) {
 		DRM_DEBUG_DRIVER("resetting chip\n");
 		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
 				   reset_event);
@@ -2480,25 +2479,9 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
 
 		intel_runtime_pm_put(dev_priv);
 
-		if (ret == 0) {
-			/*
-			 * After all the gem state is reset, increment the reset
-			 * counter and wake up everyone waiting for the reset to
-			 * complete.
-			 *
-			 * Since unlock operations are a one-sided barrier only,
-			 * we need to insert a barrier here to order any seqno
-			 * updates before
-			 * the counter increment.
-			 */
-			smp_mb__before_atomic();
-			atomic_inc(&dev_priv->gpu_error.reset_counter);
-
+		if (ret == 0)
 			kobject_uevent_env(&dev->primary->kdev->kobj,
 					   KOBJ_CHANGE, reset_done_event);
-		} else {
-			atomic_or(I915_WEDGED, &error->reset_counter);
-		}
 
 		/*
 		 * Note: The wake_up also serves as a memory barrier so that
-- 
2.6.3

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Re: [PATCH 06/32] drm/i915: Tighten reset_counter for reset status

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:02AM +0000, Chris Wilson wrote:
> In the reset_counter, we use two bits to track a GPU hang and reset. The
> low bit is a "reset-in-progress" flag that we set to signal when we need
> to break waiters in order for the recovery task to grab the mutex. As
> soon as the recovery task has the mutex, we can clear that flag (which
> we do by incrementing the reset_counter thereby incrementing the gobal
> reset epoch). By clearing that flag when the recovery task holds the
> struct_mutex, we can forgo a second flag that simply tells GEM to ignore
> the "reset-in-progress" flag.
> 
> The second flag we store in the reset_counter is whether the
> reset failed and we consider the GPU terminally wedged. Whilst this flag
> is set, all access to the GPU (at least through GEM rather than direct mmio
> access) is verboten.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/i915_debugfs.c |  4 ++--
>  drivers/gpu/drm/i915/i915_drv.c     | 39 ++++++++++++++++++++++---------------
>  drivers/gpu/drm/i915/i915_drv.h     |  3 ---
>  drivers/gpu/drm/i915/i915_gem.c     | 27 +++++++++----------------
>  drivers/gpu/drm/i915/i915_irq.c     | 21 ++------------------
>  5 files changed, 36 insertions(+), 58 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index c26a4c087f49..d5f66bbdb160 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4672,7 +4672,7 @@ i915_wedged_get(void *data, u64 *val)
>  	struct drm_device *dev = data;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  
> -	*val = i915_reset_counter(&dev_priv->gpu_error);
> +	*val = i915_terminally_wedged(&dev_priv->gpu_error);
>  
>  	return 0;
>  }
> @@ -4691,7 +4691,7 @@ i915_wedged_set(void *data, u64 val)
>  	 * while it is writing to 'i915_wedged'
>  	 */
>  
> -	if (i915_reset_in_progress_or_wedged(&dev_priv->gpu_error))
> +	if (i915_reset_in_progress(&dev_priv->gpu_error))
>  		return -EAGAIN;
>  
>  	intel_runtime_pm_get(dev_priv);
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 8ddfcce92cf1..8bdc51bc00a4 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -858,23 +858,32 @@ int i915_resume_switcheroo(struct drm_device *dev)
>  int i915_reset(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> -	bool simulated;
> +	struct i915_gpu_error *error = &dev_priv->gpu_error;
> +	unsigned reset_counter;
>  	int ret;
>  
>  	intel_reset_gt_powersave(dev);
>  
>  	mutex_lock(&dev->struct_mutex);
>  
> -	i915_gem_reset(dev);
> +	/* Clear any previous failed attempts at recovery. Time to try again. */
> +	atomic_andnot(I915_WEDGED, &error->reset_counter);
>  
> -	simulated = dev_priv->gpu_error.stop_rings != 0;
> +	/* Clear the reset-in-progress flag and increment the reset epoch. */
> +	reset_counter = atomic_inc_return(&error->reset_counter);
> +	if (WARN_ON(__i915_reset_in_progress(reset_counter))) {
> +		ret = -EIO;
> +		goto error;
> +	}
> +
> +	i915_gem_reset(dev);
>  
>  	ret = intel_gpu_reset(dev);
>  
>  	/* Also reset the gpu hangman. */
> -	if (simulated) {
> +	if (error->stop_rings != 0) {
>  		DRM_INFO("Simulated gpu hang, resetting stop_rings\n");
> -		dev_priv->gpu_error.stop_rings = 0;
> +		error->stop_rings = 0;
>  		if (ret == -ENODEV) {
>  			DRM_INFO("Reset not implemented, but ignoring "
>  				 "error for simulated gpu hangs\n");
> @@ -887,8 +896,7 @@ int i915_reset(struct drm_device *dev)
>  
>  	if (ret) {
>  		DRM_ERROR("Failed to reset chip: %i\n", ret);
> -		mutex_unlock(&dev->struct_mutex);
> -		return ret;
> +		goto error;
>  	}
>  
>  	intel_overlay_reset(dev_priv);
> @@ -907,20 +915,14 @@ int i915_reset(struct drm_device *dev)
>  	 * was running at the time of the reset (i.e. we weren't VT
>  	 * switched away).
>  	 */
> -
> -	/* Used to prevent gem_check_wedged returning -EAGAIN during gpu reset */
> -	dev_priv->gpu_error.reload_in_reset = true;
> -
>  	ret = i915_gem_init_hw(dev);
> -
> -	dev_priv->gpu_error.reload_in_reset = false;
> -
> -	mutex_unlock(&dev->struct_mutex);
>  	if (ret) {
>  		DRM_ERROR("Failed hw init on reset %d\n", ret);
> -		return ret;
> +		goto error;
>  	}
>  
> +	mutex_unlock(&dev->struct_mutex);
> +
>  	/*
>  	 * rps/rc6 re-init is necessary to restore state lost after the
>  	 * reset and the re-install of gt irqs. Skip for ironlake per
> @@ -931,6 +933,11 @@ int i915_reset(struct drm_device *dev)
>  		intel_enable_gt_powersave(dev);
>  
>  	return 0;
> +
> +error:
> +	atomic_or(I915_WEDGED, &error->reset_counter);
> +	mutex_unlock(&dev->struct_mutex);
> +	return ret;
>  }
>  
>  static int i915_pci_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 466caa0bc043..1043ddd670a5 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1384,9 +1384,6 @@ struct i915_gpu_error {
>  
>  	/* For missed irq/seqno simulation. */
>  	unsigned int test_irq_rings;
> -
> -	/* Used to prevent gem_check_wedged returning -EAGAIN during gpu reset   */
> -	bool reload_in_reset;
>  };
>  
>  enum modeset_restore {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0b3e0534baa3..27e617b76418 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -85,9 +85,7 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
>  {
>  	int ret;
>  
> -#define EXIT_COND (!i915_reset_in_progress_or_wedged(error) || \
> -		   i915_terminally_wedged(error))
> -	if (EXIT_COND)
> +	if (!i915_reset_in_progress(error))
>  		return 0;
>  
>  	/*
> @@ -96,17 +94,16 @@ i915_gem_wait_for_error(struct i915_gpu_error *error)
>  	 * we should simply try to bail out and fail as gracefully as possible.
>  	 */
>  	ret = wait_event_interruptible_timeout(error->reset_queue,
> -					       EXIT_COND,
> +					       !i915_reset_in_progress(error),
>  					       10*HZ);
>  	if (ret == 0) {
>  		DRM_ERROR("Timed out waiting for the gpu reset to complete\n");
>  		return -EIO;
>  	} else if (ret < 0) {
>  		return ret;
> +	} else {
> +		return 0;
>  	}
> -#undef EXIT_COND
> -
> -	return 0;
>  }
>  
>  int i915_mutex_lock_interruptible(struct drm_device *dev)
> @@ -1114,22 +1111,16 @@ i915_gem_check_wedge(struct i915_gpu_error *error,
>  		     bool interruptible)
>  {
>  	if (i915_reset_in_progress_or_wedged(error)) {
> +		/* Recovery complete, but the reset failed ... */
> +		if (i915_terminally_wedged(error))
> +			return -EIO;
> +
>  		/* Non-interruptible callers can't handle -EAGAIN, hence return
>  		 * -EIO unconditionally for these. */
>  		if (!interruptible)
>  			return -EIO;
>  
> -		/* Recovery complete, but the reset failed ... */
> -		if (i915_terminally_wedged(error))
> -			return -EIO;
> -
> -		/*
> -		 * Check if GPU Reset is in progress - we need intel_ring_begin
> -		 * to work properly to reinit the hw state while the gpu is
> -		 * still marked as reset-in-progress. Handle this with a flag.
> -		 */
> -		if (!error->reload_in_reset)
> -			return -EAGAIN;
> +		return -EAGAIN;
>  	}
>  
>  	return 0;
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 60dff3f89531..88206c0404d7 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -2434,7 +2434,6 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
>  static void i915_reset_and_wakeup(struct drm_device *dev)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(dev);
> -	struct i915_gpu_error *error = &dev_priv->gpu_error;
>  	char *error_event[] = { I915_ERROR_UEVENT "=1", NULL };
>  	char *reset_event[] = { I915_RESET_UEVENT "=1", NULL };
>  	char *reset_done_event[] = { I915_ERROR_UEVENT "=0", NULL };
> @@ -2452,7 +2451,7 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
>  	 * the reset in-progress bit is only ever set by code outside of this
>  	 * work we don't need to worry about any other races.
>  	 */
> -	if (i915_reset_in_progress_or_wedged(error) && !i915_terminally_wedged(error)) {
> +	if (i915_reset_in_progress(&dev_priv->gpu_error)) {
>  		DRM_DEBUG_DRIVER("resetting chip\n");
>  		kobject_uevent_env(&dev->primary->kdev->kobj, KOBJ_CHANGE,
>  				   reset_event);
> @@ -2480,25 +2479,9 @@ static void i915_reset_and_wakeup(struct drm_device *dev)
>  
>  		intel_runtime_pm_put(dev_priv);
>  
> -		if (ret == 0) {
> -			/*
> -			 * After all the gem state is reset, increment the reset
> -			 * counter and wake up everyone waiting for the reset to
> -			 * complete.
> -			 *
> -			 * Since unlock operations are a one-sided barrier only,
> -			 * we need to insert a barrier here to order any seqno
> -			 * updates before
> -			 * the counter increment.
> -			 */
> -			smp_mb__before_atomic();
> -			atomic_inc(&dev_priv->gpu_error.reset_counter);
> -
> +		if (ret == 0)
>  			kobject_uevent_env(&dev->primary->kdev->kobj,
>  					   KOBJ_CHANGE, reset_done_event);
> -		} else {
> -			atomic_or(I915_WEDGED, &error->reset_counter);
> -		}
>  
>  		/*
>  		 * Note: The wake_up also serves as a memory barrier so that
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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[PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Chris Wilson]

As the request is only valid during the same global reset epoch, we can
record the current reset_counter when constructing the request and reuse
it when waiting upon that request in future. This removes a very hairy
atomic check serialised by the struct_mutex at the time of waiting and
allows us to transfer those waits to a central dispatcher for all
waiters and all requests.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.h         |  2 +-
 drivers/gpu/drm/i915/i915_gem.c         | 40 +++++++++++----------------------
 drivers/gpu/drm/i915/intel_display.c    |  7 +-----
 drivers/gpu/drm/i915/intel_lrc.c        |  7 ------
 drivers/gpu/drm/i915/intel_ringbuffer.c |  6 -----
 5 files changed, 15 insertions(+), 47 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1043ddd670a5..f30c305a6889 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2178,6 +2178,7 @@ struct drm_i915_gem_request {
 	/** On Which ring this request was generated */
 	struct drm_i915_private *i915;
 	struct intel_engine_cs *ring;
+	unsigned reset_counter;
 
 	 /** GEM sequence number associated with the previous request,
 	  * when the HWS breadcrumb is equal to this the GPU is processing
@@ -3059,7 +3060,6 @@ void __i915_add_request(struct drm_i915_gem_request *req,
 #define i915_add_request_no_flush(req) \
 	__i915_add_request(req, NULL, false)
 int __i915_wait_request(struct drm_i915_gem_request *req,
-			unsigned reset_counter,
 			bool interruptible,
 			s64 *timeout,
 			struct intel_rps_client *rps);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 27e617b76418..b17cc0e42a4f 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1214,7 +1214,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 /**
  * __i915_wait_request - wait until execution of request has finished
  * @req: duh!
- * @reset_counter: reset sequence associated with the given request
  * @interruptible: do an interruptible wait (normally yes)
  * @timeout: in - how long to wait (NULL forever); out - how much time remaining
  *
@@ -1229,7 +1228,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
  * errno with remaining time filled in timeout argument.
  */
 int __i915_wait_request(struct drm_i915_gem_request *req,
-			unsigned reset_counter,
 			bool interruptible,
 			s64 *timeout,
 			struct intel_rps_client *rps)
@@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 
 		/* We need to check whether any gpu reset happened in between
 		 * the caller grabbing the seqno and now ... */
-		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
+		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
 			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
 			 * is truely gone. */
 			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
@@ -1461,13 +1459,7 @@ i915_wait_request(struct drm_i915_gem_request *req)
 
 	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
 
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
-	if (ret)
-		return ret;
-
-	ret = __i915_wait_request(req,
-				  i915_reset_counter(&dev_priv->gpu_error),
-				  interruptible, NULL, NULL);
+	ret = __i915_wait_request(req, interruptible, NULL, NULL);
 	if (ret)
 		return ret;
 
@@ -1542,7 +1534,6 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
 	struct drm_device *dev = obj->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_request *requests[I915_NUM_RINGS];
-	unsigned reset_counter;
 	int ret, i, n = 0;
 
 	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
@@ -1551,12 +1542,6 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
 	if (!obj->active)
 		return 0;
 
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error, true);
-	if (ret)
-		return ret;
-
-	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-
 	if (readonly) {
 		struct drm_i915_gem_request *req;
 
@@ -1578,9 +1563,9 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
 	}
 
 	mutex_unlock(&dev->struct_mutex);
+	ret = 0;
 	for (i = 0; ret == 0 && i < n; i++)
-		ret = __i915_wait_request(requests[i], reset_counter, true,
-					  NULL, rps);
+		ret = __i915_wait_request(requests[i], true, NULL, rps);
 	mutex_lock(&dev->struct_mutex);
 
 	for (i = 0; i < n; i++) {
@@ -2684,6 +2669,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 			   struct drm_i915_gem_request **req_out)
 {
 	struct drm_i915_private *dev_priv = to_i915(ring->dev);
+	unsigned reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 	struct drm_i915_gem_request *req;
 	int ret;
 
@@ -2692,6 +2678,11 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 
 	*req_out = NULL;
 
+	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
+				   dev_priv->mm.interruptible);
+	if (ret)
+		return ret;
+
 	req = kmem_cache_zalloc(dev_priv->requests, GFP_KERNEL);
 	if (req == NULL)
 		return -ENOMEM;
@@ -2703,6 +2694,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 	kref_init(&req->ref);
 	req->i915 = dev_priv;
 	req->ring = ring;
+	req->reset_counter = reset_counter;
 	req->ctx  = ctx;
 	i915_gem_context_reference(req->ctx);
 
@@ -3067,11 +3059,9 @@ retire:
 int
 i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_wait *args = data;
 	struct drm_i915_gem_object *obj;
 	struct drm_i915_gem_request *req[I915_NUM_RINGS];
-	unsigned reset_counter;
 	int i, n = 0;
 	int ret;
 
@@ -3105,7 +3095,6 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 	}
 
 	drm_gem_object_unreference(&obj->base);
-	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 
 	for (i = 0; i < I915_NUM_RINGS; i++) {
 		if (obj->last_read_req[i] == NULL)
@@ -3118,7 +3107,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 
 	for (i = 0; i < n; i++) {
 		if (ret == 0)
-			ret = __i915_wait_request(req[i], reset_counter, true,
+			ret = __i915_wait_request(req[i], true,
 						  args->timeout_ns > 0 ? &args->timeout_ns : NULL,
 						  to_rps_client(file));
 		i915_gem_request_unreference__unlocked(req[i]);
@@ -3150,7 +3139,6 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
 	if (!i915_semaphore_is_enabled(obj->base.dev)) {
 		struct drm_i915_private *i915 = to_i915(obj->base.dev);
 		ret = __i915_wait_request(from_req,
-					  i915_reset_counter(&i915->gpu_error),
 					  i915->mm.interruptible,
 					  NULL,
 					  &i915->rps.semaphores);
@@ -4099,7 +4087,6 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 	struct drm_i915_file_private *file_priv = file->driver_priv;
 	unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
 	struct drm_i915_gem_request *request, *target = NULL;
-	unsigned reset_counter;
 	int ret;
 
 	ret = i915_gem_wait_for_error(&dev_priv->gpu_error);
@@ -4124,7 +4111,6 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 
 		target = request;
 	}
-	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 	if (target)
 		i915_gem_request_reference(target);
 	spin_unlock(&file_priv->mm.lock);
@@ -4132,7 +4118,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 	if (target == NULL)
 		return 0;
 
-	ret = __i915_wait_request(target, reset_counter, true, NULL, NULL);
+	ret = __i915_wait_request(target, true, NULL, NULL);
 	if (ret == 0)
 		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);
 
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8b6028cd619f..d59beca928b7 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11394,7 +11394,6 @@ static void intel_mmio_flip_work_func(struct work_struct *work)
 
 	if (mmio_flip->req) {
 		WARN_ON(__i915_wait_request(mmio_flip->req,
-					    mmio_flip->crtc->reset_counter,
 					    false, NULL,
 					    &mmio_flip->i915->rps.mmioflips));
 		i915_gem_request_unreference__unlocked(mmio_flip->req);
@@ -13395,9 +13394,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 
 	ret = drm_atomic_helper_prepare_planes(dev, state);
 	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
-		u32 reset_counter;
-
-		reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 		mutex_unlock(&dev->struct_mutex);
 
 		for_each_plane_in_state(state, plane, plane_state, i) {
@@ -13408,8 +13404,7 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 				continue;
 
 			ret = __i915_wait_request(intel_plane_state->wait_req,
-						  reset_counter, true,
-						  NULL, NULL);
+						  true, NULL, NULL);
 
 			/* Swallow -EIO errors to allow updates during hw lockup. */
 			if (ret == -EIO)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 86404b03dc91..69b298eed69d 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -819,16 +819,9 @@ static int logical_ring_prepare(struct drm_i915_gem_request *req, int bytes)
  */
 int intel_logical_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
 {
-	struct drm_i915_private *dev_priv;
 	int ret;
 
 	WARN_ON(req == NULL);
-	dev_priv = req->ring->dev->dev_private;
-
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
-				   dev_priv->mm.interruptible);
-	if (ret)
-		return ret;
 
 	ret = logical_ring_prepare(req, num_dwords * sizeof(uint32_t));
 	if (ret)
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index d71fa77055f9..942f86b316c2 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2274,7 +2274,6 @@ int intel_ring_idle(struct intel_engine_cs *ring)
 
 	/* Make sure we do not trigger any retires */
 	return __i915_wait_request(req,
-				   i915_reset_counter(&to_i915(ring->dev)->gpu_error),
 				   to_i915(ring->dev)->mm.interruptible,
 				   NULL, NULL);
 }
@@ -2405,11 +2404,6 @@ int intel_ring_begin(struct drm_i915_gem_request *req,
 	ring = req->ring;
 	dev_priv = ring->dev->dev_private;
 
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
-				   dev_priv->mm.interruptible);
-	if (ret)
-		return ret;
-
 	ret = __intel_ring_prepare(ring, num_dwords * sizeof(uint32_t));
 	if (ret)
 		return ret;
-- 
2.6.3

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:03AM +0000, Chris Wilson wrote:
> As the request is only valid during the same global reset epoch, we can
> record the current reset_counter when constructing the request and reuse
> it when waiting upon that request in future. This removes a very hairy
> atomic check serialised by the struct_mutex at the time of waiting and
> allows us to transfer those waits to a central dispatcher for all
> waiters and all requests.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

"global reset epoch" got me thinking about what the implications for TDR
are. Now the current TDR patches iirc are still somewhat tacked on the
side of the existing reset handling, and so don't end up incrementing the
reset counter.

But I don't agree with that design decision, and I think any reset must
increment the counter (and do the reset-in-progress flag dance), since
that's the only way to guarantee that waiters will get off locks. Even
though we have fewer of those with every kernel release.

But then there's the problem that at least for some request they'll still
be valid after the reset, and would break with this design here. Which can
easily be fixed by incrementing the reset epoch for every request we
decide should keep running (or which gets re-scheduled/emitted for another
attempt), and doing that explicitly seems like a good idea.

The only implication I see is that for per-ring reset we might want to go
to a per-engine reset epoch counter.

So given all that I think this is a solid idea. But one comment below as a
fallout.

> ---
>  drivers/gpu/drm/i915/i915_drv.h         |  2 +-
>  drivers/gpu/drm/i915/i915_gem.c         | 40 +++++++++++----------------------
>  drivers/gpu/drm/i915/intel_display.c    |  7 +-----
>  drivers/gpu/drm/i915/intel_lrc.c        |  7 ------
>  drivers/gpu/drm/i915/intel_ringbuffer.c |  6 -----
>  5 files changed, 15 insertions(+), 47 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 1043ddd670a5..f30c305a6889 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2178,6 +2178,7 @@ struct drm_i915_gem_request {
>  	/** On Which ring this request was generated */
>  	struct drm_i915_private *i915;
>  	struct intel_engine_cs *ring;
> +	unsigned reset_counter;
>  
>  	 /** GEM sequence number associated with the previous request,
>  	  * when the HWS breadcrumb is equal to this the GPU is processing
> @@ -3059,7 +3060,6 @@ void __i915_add_request(struct drm_i915_gem_request *req,
>  #define i915_add_request_no_flush(req) \
>  	__i915_add_request(req, NULL, false)
>  int __i915_wait_request(struct drm_i915_gem_request *req,
> -			unsigned reset_counter,
>  			bool interruptible,
>  			s64 *timeout,
>  			struct intel_rps_client *rps);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 27e617b76418..b17cc0e42a4f 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1214,7 +1214,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>  /**
>   * __i915_wait_request - wait until execution of request has finished
>   * @req: duh!
> - * @reset_counter: reset sequence associated with the given request
>   * @interruptible: do an interruptible wait (normally yes)
>   * @timeout: in - how long to wait (NULL forever); out - how much time remaining
>   *
> @@ -1229,7 +1228,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>   * errno with remaining time filled in timeout argument.
>   */
>  int __i915_wait_request(struct drm_i915_gem_request *req,
> -			unsigned reset_counter,
>  			bool interruptible,
>  			s64 *timeout,
>  			struct intel_rps_client *rps)
> @@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  
>  		/* We need to check whether any gpu reset happened in between
>  		 * the caller grabbing the seqno and now ... */
> -		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> +		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {

READ_ONCE(req->reset) as a future proofing maybe for TDR? Or punt that to
TDR? Could be confusing to READ_ONCE something that's (with the current
code at least) invariant.

So either way: Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>


>  			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
>  			 * is truely gone. */
>  			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> @@ -1461,13 +1459,7 @@ i915_wait_request(struct drm_i915_gem_request *req)
>  
>  	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
>  
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> -	if (ret)
> -		return ret;
> -
> -	ret = __i915_wait_request(req,
> -				  i915_reset_counter(&dev_priv->gpu_error),
> -				  interruptible, NULL, NULL);
> +	ret = __i915_wait_request(req, interruptible, NULL, NULL);
>  	if (ret)
>  		return ret;
>  
> @@ -1542,7 +1534,6 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
>  	struct drm_device *dev = obj->base.dev;
>  	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_i915_gem_request *requests[I915_NUM_RINGS];
> -	unsigned reset_counter;
>  	int ret, i, n = 0;
>  
>  	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
> @@ -1551,12 +1542,6 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
>  	if (!obj->active)
>  		return 0;
>  
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error, true);
> -	if (ret)
> -		return ret;
> -
> -	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
> -
>  	if (readonly) {
>  		struct drm_i915_gem_request *req;
>  
> @@ -1578,9 +1563,9 @@ i915_gem_object_wait_rendering__nonblocking(struct drm_i915_gem_object *obj,
>  	}
>  
>  	mutex_unlock(&dev->struct_mutex);
> +	ret = 0;
>  	for (i = 0; ret == 0 && i < n; i++)
> -		ret = __i915_wait_request(requests[i], reset_counter, true,
> -					  NULL, rps);
> +		ret = __i915_wait_request(requests[i], true, NULL, rps);
>  	mutex_lock(&dev->struct_mutex);
>  
>  	for (i = 0; i < n; i++) {
> @@ -2684,6 +2669,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>  			   struct drm_i915_gem_request **req_out)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(ring->dev);
> +	unsigned reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  	struct drm_i915_gem_request *req;
>  	int ret;
>  
> @@ -2692,6 +2678,11 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>  
>  	*req_out = NULL;
>  
> +	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
> +				   dev_priv->mm.interruptible);
> +	if (ret)
> +		return ret;
> +
>  	req = kmem_cache_zalloc(dev_priv->requests, GFP_KERNEL);
>  	if (req == NULL)
>  		return -ENOMEM;
> @@ -2703,6 +2694,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>  	kref_init(&req->ref);
>  	req->i915 = dev_priv;
>  	req->ring = ring;
> +	req->reset_counter = reset_counter;
>  	req->ctx  = ctx;
>  	i915_gem_context_reference(req->ctx);
>  
> @@ -3067,11 +3059,9 @@ retire:
>  int
>  i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  {
> -	struct drm_i915_private *dev_priv = dev->dev_private;
>  	struct drm_i915_gem_wait *args = data;
>  	struct drm_i915_gem_object *obj;
>  	struct drm_i915_gem_request *req[I915_NUM_RINGS];
> -	unsigned reset_counter;
>  	int i, n = 0;
>  	int ret;
>  
> @@ -3105,7 +3095,6 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  	}
>  
>  	drm_gem_object_unreference(&obj->base);
> -	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  
>  	for (i = 0; i < I915_NUM_RINGS; i++) {
>  		if (obj->last_read_req[i] == NULL)
> @@ -3118,7 +3107,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
>  
>  	for (i = 0; i < n; i++) {
>  		if (ret == 0)
> -			ret = __i915_wait_request(req[i], reset_counter, true,
> +			ret = __i915_wait_request(req[i], true,
>  						  args->timeout_ns > 0 ? &args->timeout_ns : NULL,
>  						  to_rps_client(file));
>  		i915_gem_request_unreference__unlocked(req[i]);
> @@ -3150,7 +3139,6 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
>  	if (!i915_semaphore_is_enabled(obj->base.dev)) {
>  		struct drm_i915_private *i915 = to_i915(obj->base.dev);
>  		ret = __i915_wait_request(from_req,
> -					  i915_reset_counter(&i915->gpu_error),
>  					  i915->mm.interruptible,
>  					  NULL,
>  					  &i915->rps.semaphores);
> @@ -4099,7 +4087,6 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  	struct drm_i915_file_private *file_priv = file->driver_priv;
>  	unsigned long recent_enough = jiffies - DRM_I915_THROTTLE_JIFFIES;
>  	struct drm_i915_gem_request *request, *target = NULL;
> -	unsigned reset_counter;
>  	int ret;
>  
>  	ret = i915_gem_wait_for_error(&dev_priv->gpu_error);
> @@ -4124,7 +4111,6 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  
>  		target = request;
>  	}
> -	reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  	if (target)
>  		i915_gem_request_reference(target);
>  	spin_unlock(&file_priv->mm.lock);
> @@ -4132,7 +4118,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  	if (target == NULL)
>  		return 0;
>  
> -	ret = __i915_wait_request(target, reset_counter, true, NULL, NULL);
> +	ret = __i915_wait_request(target, true, NULL, NULL);
>  	if (ret == 0)
>  		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);
>  
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 8b6028cd619f..d59beca928b7 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -11394,7 +11394,6 @@ static void intel_mmio_flip_work_func(struct work_struct *work)
>  
>  	if (mmio_flip->req) {
>  		WARN_ON(__i915_wait_request(mmio_flip->req,
> -					    mmio_flip->crtc->reset_counter,
>  					    false, NULL,
>  					    &mmio_flip->i915->rps.mmioflips));
>  		i915_gem_request_unreference__unlocked(mmio_flip->req);
> @@ -13395,9 +13394,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  
>  	ret = drm_atomic_helper_prepare_planes(dev, state);
>  	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
> -		u32 reset_counter;
> -
> -		reset_counter = i915_reset_counter(&dev_priv->gpu_error);
>  		mutex_unlock(&dev->struct_mutex);
>  
>  		for_each_plane_in_state(state, plane, plane_state, i) {
> @@ -13408,8 +13404,7 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  				continue;
>  
>  			ret = __i915_wait_request(intel_plane_state->wait_req,
> -						  reset_counter, true,
> -						  NULL, NULL);
> +						  true, NULL, NULL);
>  
>  			/* Swallow -EIO errors to allow updates during hw lockup. */
>  			if (ret == -EIO)
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 86404b03dc91..69b298eed69d 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -819,16 +819,9 @@ static int logical_ring_prepare(struct drm_i915_gem_request *req, int bytes)
>   */
>  int intel_logical_ring_begin(struct drm_i915_gem_request *req, int num_dwords)
>  {
> -	struct drm_i915_private *dev_priv;
>  	int ret;
>  
>  	WARN_ON(req == NULL);
> -	dev_priv = req->ring->dev->dev_private;
> -
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
> -				   dev_priv->mm.interruptible);
> -	if (ret)
> -		return ret;
>  
>  	ret = logical_ring_prepare(req, num_dwords * sizeof(uint32_t));
>  	if (ret)
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index d71fa77055f9..942f86b316c2 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2274,7 +2274,6 @@ int intel_ring_idle(struct intel_engine_cs *ring)
>  
>  	/* Make sure we do not trigger any retires */
>  	return __i915_wait_request(req,
> -				   i915_reset_counter(&to_i915(ring->dev)->gpu_error),
>  				   to_i915(ring->dev)->mm.interruptible,
>  				   NULL, NULL);
>  }
> @@ -2405,11 +2404,6 @@ int intel_ring_begin(struct drm_i915_gem_request *req,
>  	ring = req->ring;
>  	dev_priv = ring->dev->dev_private;
>  
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
> -				   dev_priv->mm.interruptible);
> -	if (ret)
> -		return ret;
> -
>  	ret = __intel_ring_prepare(ring, num_dwords * sizeof(uint32_t));
>  	if (ret)
>  		return ret;
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Re: [PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Chris Wilson]

On Wed, Dec 16, 2015 at 10:44:19AM +0100, Daniel Vetter wrote:
> On Fri, Dec 11, 2015 at 11:33:03AM +0000, Chris Wilson wrote:
> > As the request is only valid during the same global reset epoch, we can
> > record the current reset_counter when constructing the request and reuse
> > it when waiting upon that request in future. This removes a very hairy
> > atomic check serialised by the struct_mutex at the time of waiting and
> > allows us to transfer those waits to a central dispatcher for all
> > waiters and all requests.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> "global reset epoch" got me thinking about what the implications for TDR
> are. Now the current TDR patches iirc are still somewhat tacked on the
> side of the existing reset handling, and so don't end up incrementing the
> reset counter.
> 
> But I don't agree with that design decision, and I think any reset must
> increment the counter (and do the reset-in-progress flag dance), since
> that's the only way to guarantee that waiters will get off locks. Even
> though we have fewer of those with every kernel release.
> 
> But then there's the problem that at least for some request they'll still
> be valid after the reset, and would break with this design here. Which can
> easily be fixed by incrementing the reset epoch for every request we
> decide should keep running (or which gets re-scheduled/emitted for another
> attempt), and doing that explicitly seems like a good idea.
> 
> The only implication I see is that for per-ring reset we might want to go
> to a per-engine reset epoch counter.

Yes, I think per-engine epoch's will be required. (I've been trying to
choose my words carefully so that it is clear that it only applies to
today and not in a TDR future!)

> So given all that I think this is a solid idea. But one comment below as a
> fallout.
> 
> > ---
> >  drivers/gpu/drm/i915/i915_drv.h         |  2 +-
> >  drivers/gpu/drm/i915/i915_gem.c         | 40 +++++++++++----------------------
> >  drivers/gpu/drm/i915/intel_display.c    |  7 +-----
> >  drivers/gpu/drm/i915/intel_lrc.c        |  7 ------
> >  drivers/gpu/drm/i915/intel_ringbuffer.c |  6 -----
> >  5 files changed, 15 insertions(+), 47 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> > index 1043ddd670a5..f30c305a6889 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.h
> > +++ b/drivers/gpu/drm/i915/i915_drv.h
> > @@ -2178,6 +2178,7 @@ struct drm_i915_gem_request {
> >  	/** On Which ring this request was generated */
> >  	struct drm_i915_private *i915;
> >  	struct intel_engine_cs *ring;
> > +	unsigned reset_counter;
> >  
> >  	 /** GEM sequence number associated with the previous request,
> >  	  * when the HWS breadcrumb is equal to this the GPU is processing
> > @@ -3059,7 +3060,6 @@ void __i915_add_request(struct drm_i915_gem_request *req,
> >  #define i915_add_request_no_flush(req) \
> >  	__i915_add_request(req, NULL, false)
> >  int __i915_wait_request(struct drm_i915_gem_request *req,
> > -			unsigned reset_counter,
> >  			bool interruptible,
> >  			s64 *timeout,
> >  			struct intel_rps_client *rps);
> > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > index 27e617b76418..b17cc0e42a4f 100644
> > --- a/drivers/gpu/drm/i915/i915_gem.c
> > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > @@ -1214,7 +1214,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
> >  /**
> >   * __i915_wait_request - wait until execution of request has finished
> >   * @req: duh!
> > - * @reset_counter: reset sequence associated with the given request
> >   * @interruptible: do an interruptible wait (normally yes)
> >   * @timeout: in - how long to wait (NULL forever); out - how much time remaining
> >   *
> > @@ -1229,7 +1228,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
> >   * errno with remaining time filled in timeout argument.
> >   */
> >  int __i915_wait_request(struct drm_i915_gem_request *req,
> > -			unsigned reset_counter,
> >  			bool interruptible,
> >  			s64 *timeout,
> >  			struct intel_rps_client *rps)
> > @@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
> >  
> >  		/* We need to check whether any gpu reset happened in between
> >  		 * the caller grabbing the seqno and now ... */
> > -		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> > +		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> 
> READ_ONCE(req->reset) as a future proofing maybe for TDR? Or punt that to
> TDR? Could be confusing to READ_ONCE something that's (with the current
> code at least) invariant.

Right, my plan was to solve this in TDR! At the moment, I am thinking
that we regenerate a new request for each one resubmitted (that requires
patching the seqno embedded into the ring before restarting the ring),
but otherwise we can just duplicate the contents of the request.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Dave Gordon]

On 16/12/15 10:19, Chris Wilson wrote:
> On Wed, Dec 16, 2015 at 10:44:19AM +0100, Daniel Vetter wrote:
>> On Fri, Dec 11, 2015 at 11:33:03AM +0000, Chris Wilson wrote:
>>> As the request is only valid during the same global reset epoch, we can
>>> record the current reset_counter when constructing the request and reuse
>>> it when waiting upon that request in future. This removes a very hairy
>>> atomic check serialised by the struct_mutex at the time of waiting and
>>> allows us to transfer those waits to a central dispatcher for all
>>> waiters and all requests.
>>>
>>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>>
>> "global reset epoch" got me thinking about what the implications for TDR
>> are. Now the current TDR patches iirc are still somewhat tacked on the
>> side of the existing reset handling, and so don't end up incrementing the
>> reset counter.
>>
>> But I don't agree with that design decision, and I think any reset must
>> increment the counter (and do the reset-in-progress flag dance), since
>> that's the only way to guarantee that waiters will get off locks. Even
>> though we have fewer of those with every kernel release.
>>
>> But then there's the problem that at least for some request they'll still
>> be valid after the reset, and would break with this design here. Which can
>> easily be fixed by incrementing the reset epoch for every request we
>> decide should keep running (or which gets re-scheduled/emitted for another
>> attempt), and doing that explicitly seems like a good idea.
>>
>> The only implication I see is that for per-ring reset we might want to go
>> to a per-engine reset epoch counter.
>
> Yes, I think per-engine epoch's will be required. (I've been trying to
> choose my words carefully so that it is clear that it only applies to
> today and not in a TDR future!)
>
>> So given all that I think this is a solid idea. But one comment below as a
>> fallout.
>>
>>> ---
>>>   drivers/gpu/drm/i915/i915_drv.h         |  2 +-
>>>   drivers/gpu/drm/i915/i915_gem.c         | 40 +++++++++++----------------------
>>>   drivers/gpu/drm/i915/intel_display.c    |  7 +-----
>>>   drivers/gpu/drm/i915/intel_lrc.c        |  7 ------
>>>   drivers/gpu/drm/i915/intel_ringbuffer.c |  6 -----
>>>   5 files changed, 15 insertions(+), 47 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>>> index 1043ddd670a5..f30c305a6889 100644
>>> --- a/drivers/gpu/drm/i915/i915_drv.h
>>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>>> @@ -2178,6 +2178,7 @@ struct drm_i915_gem_request {
>>>   	/** On Which ring this request was generated */
>>>   	struct drm_i915_private *i915;
>>>   	struct intel_engine_cs *ring;
>>> +	unsigned reset_counter;
>>>
>>>   	 /** GEM sequence number associated with the previous request,
>>>   	  * when the HWS breadcrumb is equal to this the GPU is processing
>>> @@ -3059,7 +3060,6 @@ void __i915_add_request(struct drm_i915_gem_request *req,
>>>   #define i915_add_request_no_flush(req) \
>>>   	__i915_add_request(req, NULL, false)
>>>   int __i915_wait_request(struct drm_i915_gem_request *req,
>>> -			unsigned reset_counter,
>>>   			bool interruptible,
>>>   			s64 *timeout,
>>>   			struct intel_rps_client *rps);
>>> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
>>> index 27e617b76418..b17cc0e42a4f 100644
>>> --- a/drivers/gpu/drm/i915/i915_gem.c
>>> +++ b/drivers/gpu/drm/i915/i915_gem.c
>>> @@ -1214,7 +1214,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>>>   /**
>>>    * __i915_wait_request - wait until execution of request has finished
>>>    * @req: duh!
>>> - * @reset_counter: reset sequence associated with the given request
>>>    * @interruptible: do an interruptible wait (normally yes)
>>>    * @timeout: in - how long to wait (NULL forever); out - how much time remaining
>>>    *
>>> @@ -1229,7 +1228,6 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>>>    * errno with remaining time filled in timeout argument.
>>>    */
>>>   int __i915_wait_request(struct drm_i915_gem_request *req,
>>> -			unsigned reset_counter,
>>>   			bool interruptible,
>>>   			s64 *timeout,
>>>   			struct intel_rps_client *rps)
>>> @@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>>>
>>>   		/* We need to check whether any gpu reset happened in between
>>>   		 * the caller grabbing the seqno and now ... */
>>> -		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
>>> +		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
>>
>> READ_ONCE(req->reset) as a future proofing maybe for TDR? Or punt that to
>> TDR? Could be confusing to READ_ONCE something that's (with the current
>> code at least) invariant.
>
> Right, my plan was to solve this in TDR! At the moment, I am thinking
> that we regenerate a new request for each one resubmitted (that requires
> patching the seqno embedded into the ring before restarting the ring),
> but otherwise we can just duplicate the contents of the request.
> -Chris

With the scheduler, there's no need to patch the contents of the 
ringbuffer; we just reset it (so it's empty) and then have the scheduler 
re-emit the requests, starting after the one that hung.

.Dave.
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Re: [PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Chris Wilson]

On Mon, Jan 04, 2016 at 03:58:21PM +0000, Dave Gordon wrote:
> On 16/12/15 10:19, Chris Wilson wrote:
> >On Wed, Dec 16, 2015 at 10:44:19AM +0100, Daniel Vetter wrote:
> >>On Fri, Dec 11, 2015 at 11:33:03AM +0000, Chris Wilson wrote:
> >>>@@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
> >>>
> >>>  		/* We need to check whether any gpu reset happened in between
> >>>  		 * the caller grabbing the seqno and now ... */
> >>>-		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> >>>+		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> >>
> >>READ_ONCE(req->reset) as a future proofing maybe for TDR? Or punt that to
> >>TDR? Could be confusing to READ_ONCE something that's (with the current
> >>code at least) invariant.
> >
> >Right, my plan was to solve this in TDR! At the moment, I am thinking
> >that we regenerate a new request for each one resubmitted (that requires
> >patching the seqno embedded into the ring before restarting the ring),
> >but otherwise we can just duplicate the contents of the request.
> 
> With the scheduler, there's no need to patch the contents of the
> ringbuffer; we just reset it (so it's empty) and then have the
> scheduler re-emit the requests, starting after the one that hung.

Which breaks __i915_wait_request, since it has already noticed that the
reset counter has changed. Hence the discussion.
-Chris

-- 
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Re: [PATCH 07/32] drm/i915: Store the reset counter when constructing a request

[Dave Gordon]

On 04/01/16 16:10, Chris Wilson wrote:
> On Mon, Jan 04, 2016 at 03:58:21PM +0000, Dave Gordon wrote:
>> On 16/12/15 10:19, Chris Wilson wrote:
>>> On Wed, Dec 16, 2015 at 10:44:19AM +0100, Daniel Vetter wrote:
>>>> On Fri, Dec 11, 2015 at 11:33:03AM +0000, Chris Wilson wrote:
>>>>> @@ -1288,7 +1286,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>>>>>
>>>>>   		/* We need to check whether any gpu reset happened in between
>>>>>   		 * the caller grabbing the seqno and now ... */
>>>>> -		if (reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
>>>>> +		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
>>>>
>>>> READ_ONCE(req->reset) as a future proofing maybe for TDR? Or punt that to
>>>> TDR? Could be confusing to READ_ONCE something that's (with the current
>>>> code at least) invariant.
>>>
>>> Right, my plan was to solve this in TDR! At the moment, I am thinking
>>> that we regenerate a new request for each one resubmitted (that requires
>>> patching the seqno embedded into the ring before restarting the ring),
>>> but otherwise we can just duplicate the contents of the request.
>>
>> With the scheduler, there's no need to patch the contents of the
>> ringbuffer; we just reset it (so it's empty) and then have the
>> scheduler re-emit the requests, starting after the one that hung.
>
> Which breaks __i915_wait_request, since it has already noticed that the
> reset counter has changed. Hence the discussion.
> -Chris

No, I'm saying that it's simpler for TDR to update the requests that are 
going to be re-emitted into an empty ring, rather than patch up the 
ringbuffer contents. Then by the time those requests reach 
__i915_wait_request() they will be seen as within the "current reset 
epoch" and proceed normally. I don't think there's any need to generate 
any new (duplicate) requests.

But maybe you can't take this approach without the scheduler ...

.Dave.
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[PATCH 08/32] drm/i915: Simplify reset_counter handling during atomic modesetting

[Chris Wilson]

Now that the reset_counter is stored on the request, we can rearrange
the code to handle reading the counter versus waiting during the atomic
modesetting for readibility (by deleting the hairiest of codes).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_display.c | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d59beca928b7..d7bbd015de35 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13393,9 +13393,9 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 		return ret;
 
 	ret = drm_atomic_helper_prepare_planes(dev, state);
-	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
-		mutex_unlock(&dev->struct_mutex);
+	mutex_unlock(&dev->struct_mutex);
 
+	if (!ret && !async) {
 		for_each_plane_in_state(state, plane, plane_state, i) {
 			struct intel_plane_state *intel_plane_state =
 				to_intel_plane_state(plane_state);
@@ -13409,19 +13409,15 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 			/* Swallow -EIO errors to allow updates during hw lockup. */
 			if (ret == -EIO)
 				ret = 0;
-
-			if (ret)
+			if (ret) {
+				mutex_lock(&dev->struct_mutex);
+				drm_atomic_helper_cleanup_planes(dev, state);
+				mutex_unlock(&dev->struct_mutex);
 				break;
+			}
 		}
-
-		if (!ret)
-			return 0;
-
-		mutex_lock(&dev->struct_mutex);
-		drm_atomic_helper_cleanup_planes(dev, state);
 	}
 
-	mutex_unlock(&dev->struct_mutex);
 	return ret;
 }
 
-- 
2.6.3

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Re: [PATCH 08/32] drm/i915: Simplify reset_counter handling during atomic modesetting

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:04AM +0000, Chris Wilson wrote:
> Now that the reset_counter is stored on the request, we can rearrange
> the code to handle reading the counter versus waiting during the atomic
> modesetting for readibility (by deleting the hairiest of codes).
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

Much better encapsulation of gem internals indeed.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/gpu/drm/i915/intel_display.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index d59beca928b7..d7bbd015de35 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13393,9 +13393,9 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  		return ret;
>  
>  	ret = drm_atomic_helper_prepare_planes(dev, state);
> -	if (!ret && !async && !i915_reset_in_progress_or_wedged(&dev_priv->gpu_error)) {
> -		mutex_unlock(&dev->struct_mutex);
> +	mutex_unlock(&dev->struct_mutex);
>  
> +	if (!ret && !async) {
>  		for_each_plane_in_state(state, plane, plane_state, i) {
>  			struct intel_plane_state *intel_plane_state =
>  				to_intel_plane_state(plane_state);
> @@ -13409,19 +13409,15 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  			/* Swallow -EIO errors to allow updates during hw lockup. */
>  			if (ret == -EIO)
>  				ret = 0;
> -
> -			if (ret)
> +			if (ret) {
> +				mutex_lock(&dev->struct_mutex);
> +				drm_atomic_helper_cleanup_planes(dev, state);
> +				mutex_unlock(&dev->struct_mutex);
>  				break;
> +			}
>  		}
> -
> -		if (!ret)
> -			return 0;
> -
> -		mutex_lock(&dev->struct_mutex);
> -		drm_atomic_helper_cleanup_planes(dev, state);
>  	}
>  
> -	mutex_unlock(&dev->struct_mutex);
>  	return ret;
>  }
>  
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 09/32] drm/i915: Prevent leaking of -EIO from i915_wait_request()

[Chris Wilson]

Reporting -EIO from i915_wait_request() has proven very troublematic
over the years, with numerous hard-to-reproduce bugs cropping up in the
corner case of where a reset occurs and the code wasn't expecting such
an error.

If the we reset the GPU or have detected a hang and wish to reset the
GPU, the request is forcibly complete and the wait broken. Currently, we
report either -EAGAIN or -EIO in order for the caller to retreat and
restart the wait (if appropriate) after dropping and then reacquiring
the struct_mutex (essential to allow the GPU reset to proceed). However,
if we take the view that the request is complete (no further work will
be done on it by the GPU because it is dead and soon to be reset), then
we can proceed with the task at hand and then drop the struct_mutex
allowing the reset to occur. This transfers the burden of checking
whether it is safe to proceed to the caller, which in all but one
instance it is safe - completely eliminating the source of all spurious
-EIO.

Of note, we only have two API entry points where we expect that
userspace can observe an EIO. First is when submitting an execbuf, if
the GPU is terminally wedged, then the operation cannot succeed and an
-EIO is reported. Secondly, existing userspace uses the throttle ioctl
to detect an already wedged GPU before starting using HW acceleration
(or to confirm that the GPU is wedged after an error condition). So if
the GPU is wedged when the user calls throttle, also report -EIO.

v2: Split more carefully the change to i915_wait_request() and assorted
ABI from the reset handling.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.h         |  2 --
 drivers/gpu/drm/i915/i915_gem.c         | 44 ++++++++++++++++-----------------
 drivers/gpu/drm/i915/i915_gem_userptr.c |  6 ++---
 drivers/gpu/drm/i915/intel_display.c    |  8 +-----
 drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c |  2 +-
 6 files changed, 27 insertions(+), 37 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f30c305a6889..7acbc072973a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2987,8 +2987,6 @@ i915_gem_find_active_request(struct intel_engine_cs *ring);
 
 bool i915_gem_retire_requests(struct drm_device *dev);
 void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
-int __must_check i915_gem_check_wedge(struct i915_gpu_error *error,
-				      bool interruptible);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)
 {
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index b17cc0e42a4f..f5760869a17c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -208,11 +208,10 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj)
 	BUG_ON(obj->madv == __I915_MADV_PURGED);
 
 	ret = i915_gem_object_set_to_cpu_domain(obj, true);
-	if (ret) {
+	if (WARN_ON(ret)) {
 		/* In the event of a disaster, abandon all caches and
 		 * hope for the best.
 		 */
-		WARN_ON(ret != -EIO);
 		obj->base.read_domains = obj->base.write_domain = I915_GEM_DOMAIN_CPU;
 	}
 
@@ -1106,15 +1105,13 @@ put_rpm:
 	return ret;
 }
 
-int
-i915_gem_check_wedge(struct i915_gpu_error *error,
-		     bool interruptible)
+static int
+i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
 {
-	if (i915_reset_in_progress_or_wedged(error)) {
-		/* Recovery complete, but the reset failed ... */
-		if (i915_terminally_wedged(error))
-			return -EIO;
+	if (__i915_terminally_wedged(reset_counter))
+		return -EIO;
 
+	if (__i915_reset_in_progress(reset_counter)) {
 		/* Non-interruptible callers can't handle -EAGAIN, hence return
 		 * -EIO unconditionally for these. */
 		if (!interruptible)
@@ -1285,13 +1282,14 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 		prepare_to_wait(&ring->irq_queue, &wait, state);
 
 		/* We need to check whether any gpu reset happened in between
-		 * the caller grabbing the seqno and now ... */
+		 * the request being submitted and now. If a reset has occurred,
+		 * the request is effectively complete (we either are in the
+		 * process of or have discarded the rendering and completely
+		 * reset the GPU. The results of the request are lost and we
+		 * are free to continue on with the original operation.
+		 */
 		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
-			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
-			 * is truely gone. */
-			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
-			if (ret == 0)
-				ret = -EAGAIN;
+			ret = 0;
 			break;
 		}
 
@@ -2154,11 +2152,10 @@ i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
 	BUG_ON(obj->madv == __I915_MADV_PURGED);
 
 	ret = i915_gem_object_set_to_cpu_domain(obj, true);
-	if (ret) {
+	if (WARN_ON(ret)) {
 		/* In the event of a disaster, abandon all caches and
 		 * hope for the best.
 		 */
-		WARN_ON(ret != -EIO);
 		i915_gem_clflush_object(obj, true);
 		obj->base.read_domains = obj->base.write_domain = I915_GEM_DOMAIN_CPU;
 	}
@@ -2678,8 +2675,11 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 
 	*req_out = NULL;
 
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
-				   dev_priv->mm.interruptible);
+	/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
+	 * EIO if the GPU is already wedged, or EAGAIN to drop the struct_mutex
+	 * and restart.
+	 */
+	ret = i915_gem_check_wedge(reset_counter, dev_priv->mm.interruptible);
 	if (ret)
 		return ret;
 
@@ -4093,9 +4093,9 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 	if (ret)
 		return ret;
 
-	ret = i915_gem_check_wedge(&dev_priv->gpu_error, false);
-	if (ret)
-		return ret;
+	/* ABI: return -EIO if already wedged */
+	if (i915_terminally_wedged(&dev_priv->gpu_error))
+		return -EIO;
 
 	spin_lock(&file_priv->mm.lock);
 	list_for_each_entry(request, &file_priv->mm.request_list, client_list) {
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index 19fb0bddc1cd..1a5f89dba4af 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -81,10 +81,8 @@ static void __cancel_userptr__worker(struct work_struct *work)
 		was_interruptible = dev_priv->mm.interruptible;
 		dev_priv->mm.interruptible = false;
 
-		list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link) {
-			int ret = i915_vma_unbind(vma);
-			WARN_ON(ret && ret != -EIO);
-		}
+		list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link)
+			WARN_ON(i915_vma_unbind(vma));
 		WARN_ON(i915_gem_object_put_pages(obj));
 
 		dev_priv->mm.interruptible = was_interruptible;
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index d7bbd015de35..875bdf814d73 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13405,10 +13405,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
 
 			ret = __i915_wait_request(intel_plane_state->wait_req,
 						  true, NULL, NULL);
-
-			/* Swallow -EIO errors to allow updates during hw lockup. */
-			if (ret == -EIO)
-				ret = 0;
 			if (ret) {
 				mutex_lock(&dev->struct_mutex);
 				drm_atomic_helper_cleanup_planes(dev, state);
@@ -13744,9 +13740,7 @@ intel_prepare_plane_fb(struct drm_plane *plane,
 		 */
 		if (needs_modeset(crtc_state))
 			ret = i915_gem_object_wait_rendering(old_obj, true);
-
-		/* Swallow -EIO errors to allow updates during hw lockup. */
-		if (ret && ret != -EIO)
+		if (ret)
 			return ret;
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 69b298eed69d..7030ff526941 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -976,7 +976,7 @@ void intel_logical_ring_stop(struct intel_engine_cs *ring)
 		return;
 
 	ret = intel_ring_idle(ring);
-	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
+	if (ret)
 		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
 			  ring->name, ret);
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 942f86b316c2..6cecc15ec01b 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -3062,7 +3062,7 @@ intel_stop_ring_buffer(struct intel_engine_cs *ring)
 		return;
 
 	ret = intel_ring_idle(ring);
-	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
+	if (ret)
 		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
 			  ring->name, ret);
 
-- 
2.6.3

_______________________________________________
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Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 09/32] drm/i915: Prevent leaking of -EIO from i915_wait_request()

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:05AM +0000, Chris Wilson wrote:
> Reporting -EIO from i915_wait_request() has proven very troublematic
> over the years, with numerous hard-to-reproduce bugs cropping up in the
> corner case of where a reset occurs and the code wasn't expecting such
> an error.
> 
> If the we reset the GPU or have detected a hang and wish to reset the
> GPU, the request is forcibly complete and the wait broken. Currently, we
> report either -EAGAIN or -EIO in order for the caller to retreat and
> restart the wait (if appropriate) after dropping and then reacquiring
> the struct_mutex (essential to allow the GPU reset to proceed). However,
> if we take the view that the request is complete (no further work will
> be done on it by the GPU because it is dead and soon to be reset), then
> we can proceed with the task at hand and then drop the struct_mutex
> allowing the reset to occur. This transfers the burden of checking
> whether it is safe to proceed to the caller, which in all but one
> instance it is safe - completely eliminating the source of all spurious
> -EIO.
> 
> Of note, we only have two API entry points where we expect that
> userspace can observe an EIO. First is when submitting an execbuf, if
> the GPU is terminally wedged, then the operation cannot succeed and an
> -EIO is reported. Secondly, existing userspace uses the throttle ioctl
> to detect an already wedged GPU before starting using HW acceleration
> (or to confirm that the GPU is wedged after an error condition). So if
> the GPU is wedged when the user calls throttle, also report -EIO.
> 
> v2: Split more carefully the change to i915_wait_request() and assorted
> ABI from the reset handling.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_drv.h         |  2 --
>  drivers/gpu/drm/i915/i915_gem.c         | 44 ++++++++++++++++-----------------
>  drivers/gpu/drm/i915/i915_gem_userptr.c |  6 ++---
>  drivers/gpu/drm/i915/intel_display.c    |  8 +-----
>  drivers/gpu/drm/i915/intel_lrc.c        |  2 +-
>  drivers/gpu/drm/i915/intel_ringbuffer.c |  2 +-
>  6 files changed, 27 insertions(+), 37 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index f30c305a6889..7acbc072973a 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2987,8 +2987,6 @@ i915_gem_find_active_request(struct intel_engine_cs *ring);
>  
>  bool i915_gem_retire_requests(struct drm_device *dev);
>  void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
> -int __must_check i915_gem_check_wedge(struct i915_gpu_error *error,
> -				      bool interruptible);
>  
>  static inline u32 i915_reset_counter(struct i915_gpu_error *error)
>  {
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index b17cc0e42a4f..f5760869a17c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -208,11 +208,10 @@ i915_gem_object_put_pages_phys(struct drm_i915_gem_object *obj)
>  	BUG_ON(obj->madv == __I915_MADV_PURGED);
>  
>  	ret = i915_gem_object_set_to_cpu_domain(obj, true);
> -	if (ret) {
> +	if (WARN_ON(ret)) {
>  		/* In the event of a disaster, abandon all caches and
>  		 * hope for the best.
>  		 */
> -		WARN_ON(ret != -EIO);
>  		obj->base.read_domains = obj->base.write_domain = I915_GEM_DOMAIN_CPU;
>  	}
>  
> @@ -1106,15 +1105,13 @@ put_rpm:
>  	return ret;
>  }
>  
> -int
> -i915_gem_check_wedge(struct i915_gpu_error *error,
> -		     bool interruptible)
> +static int
> +i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
>  {
> -	if (i915_reset_in_progress_or_wedged(error)) {
> -		/* Recovery complete, but the reset failed ... */
> -		if (i915_terminally_wedged(error))
> -			return -EIO;
> +	if (__i915_terminally_wedged(reset_counter))
> +		return -EIO;
>  
> +	if (__i915_reset_in_progress(reset_counter)) {
>  		/* Non-interruptible callers can't handle -EAGAIN, hence return
>  		 * -EIO unconditionally for these. */
>  		if (!interruptible)
> @@ -1285,13 +1282,14 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>  		prepare_to_wait(&ring->irq_queue, &wait, state);
>  
>  		/* We need to check whether any gpu reset happened in between
> -		 * the caller grabbing the seqno and now ... */
> +		 * the request being submitted and now. If a reset has occurred,
> +		 * the request is effectively complete (we either are in the
> +		 * process of or have discarded the rendering and completely
> +		 * reset the GPU. The results of the request are lost and we
> +		 * are free to continue on with the original operation.
> +		 */
>  		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> -			/* ... but upgrade the -EAGAIN to an -EIO if the gpu
> -			 * is truely gone. */
> -			ret = i915_gem_check_wedge(&dev_priv->gpu_error, interruptible);
> -			if (ret == 0)
> -				ret = -EAGAIN;
> +			ret = 0;
>  			break;
>  		}
>  
> @@ -2154,11 +2152,10 @@ i915_gem_object_put_pages_gtt(struct drm_i915_gem_object *obj)
>  	BUG_ON(obj->madv == __I915_MADV_PURGED);
>  
>  	ret = i915_gem_object_set_to_cpu_domain(obj, true);
> -	if (ret) {
> +	if (WARN_ON(ret)) {
>  		/* In the event of a disaster, abandon all caches and
>  		 * hope for the best.
>  		 */
> -		WARN_ON(ret != -EIO);
>  		i915_gem_clflush_object(obj, true);
>  		obj->base.read_domains = obj->base.write_domain = I915_GEM_DOMAIN_CPU;
>  	}
> @@ -2678,8 +2675,11 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
>  
>  	*req_out = NULL;
>  
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error,
> -				   dev_priv->mm.interruptible);
> +	/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
> +	 * EIO if the GPU is already wedged, or EAGAIN to drop the struct_mutex
> +	 * and restart.
> +	 */
> +	ret = i915_gem_check_wedge(reset_counter, dev_priv->mm.interruptible);
>  	if (ret)
>  		return ret;
>  
> @@ -4093,9 +4093,9 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
>  	if (ret)
>  		return ret;
>  
> -	ret = i915_gem_check_wedge(&dev_priv->gpu_error, false);
> -	if (ret)
> -		return ret;
> +	/* ABI: return -EIO if already wedged */
> +	if (i915_terminally_wedged(&dev_priv->gpu_error))
> +		return -EIO;
>  
>  	spin_lock(&file_priv->mm.lock);
>  	list_for_each_entry(request, &file_priv->mm.request_list, client_list) {
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 19fb0bddc1cd..1a5f89dba4af 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -81,10 +81,8 @@ static void __cancel_userptr__worker(struct work_struct *work)
>  		was_interruptible = dev_priv->mm.interruptible;
>  		dev_priv->mm.interruptible = false;
>  
> -		list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link) {
> -			int ret = i915_vma_unbind(vma);
> -			WARN_ON(ret && ret != -EIO);
> -		}
> +		list_for_each_entry_safe(vma, tmp, &obj->vma_list, vma_link)
> +			WARN_ON(i915_vma_unbind(vma));
>  		WARN_ON(i915_gem_object_put_pages(obj));
>  
>  		dev_priv->mm.interruptible = was_interruptible;
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index d7bbd015de35..875bdf814d73 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13405,10 +13405,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>  
>  			ret = __i915_wait_request(intel_plane_state->wait_req,
>  						  true, NULL, NULL);
> -
> -			/* Swallow -EIO errors to allow updates during hw lockup. */
> -			if (ret == -EIO)

I'd like to keep a WARN_ON here since it's ABI relevant, and consistent
with the other places we've had a WARN_ON(-EIO).

> -				ret = 0;
>  			if (ret) {
>  				mutex_lock(&dev->struct_mutex);
>  				drm_atomic_helper_cleanup_planes(dev, state);
> @@ -13744,9 +13740,7 @@ intel_prepare_plane_fb(struct drm_plane *plane,
>  		 */
>  		if (needs_modeset(crtc_state))
>  			ret = i915_gem_object_wait_rendering(old_obj, true);
> -
> -		/* Swallow -EIO errors to allow updates during hw lockup. */
> -		if (ret && ret != -EIO)
> +		if (ret)

Same here really.

We already have a WARN_ON in the mmio_flip, so are covered there already.

Otherwise looks good, and with the above addressed and under the
assumption that the last caller of check_wedge is in request_alloc (which
I was too lazy to check perfectly):

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>  			return ret;
>  	}
>  
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 69b298eed69d..7030ff526941 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -976,7 +976,7 @@ void intel_logical_ring_stop(struct intel_engine_cs *ring)
>  		return;
>  
>  	ret = intel_ring_idle(ring);
> -	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
> +	if (ret)
>  		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
>  			  ring->name, ret);
>  
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 942f86b316c2..6cecc15ec01b 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -3062,7 +3062,7 @@ intel_stop_ring_buffer(struct intel_engine_cs *ring)
>  		return;
>  
>  	ret = intel_ring_idle(ring);
> -	if (ret && !i915_reset_in_progress_or_wedged(&to_i915(ring->dev)->gpu_error))
> +	if (ret)
>  		DRM_ERROR("failed to quiesce %s whilst cleaning up: %d\n",
>  			  ring->name, ret);
>  
> -- 
> 2.6.3
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 09/32] drm/i915: Prevent leaking of -EIO from i915_wait_request()

[Chris Wilson]

On Wed, Dec 16, 2015 at 10:52:06AM +0100, Daniel Vetter wrote:
> On Fri, Dec 11, 2015 at 11:33:05AM +0000, Chris Wilson wrote:
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index d7bbd015de35..875bdf814d73 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -13405,10 +13405,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
> >  
> >  			ret = __i915_wait_request(intel_plane_state->wait_req,
> >  						  true, NULL, NULL);
> > -
> > -			/* Swallow -EIO errors to allow updates during hw lockup. */
> > -			if (ret == -EIO)
> 
> I'd like to keep a WARN_ON here since it's ABI relevant, and consistent
> with the other places we've had a WARN_ON(-EIO).
> 
> > -				ret = 0;
> >  			if (ret) {
> >  				mutex_lock(&dev->struct_mutex);
> >  				drm_atomic_helper_cleanup_planes(dev, state);
> > @@ -13744,9 +13740,7 @@ intel_prepare_plane_fb(struct drm_plane *plane,
> >  		 */
> >  		if (needs_modeset(crtc_state))
> >  			ret = i915_gem_object_wait_rendering(old_obj, true);
> > -
> > -		/* Swallow -EIO errors to allow updates during hw lockup. */
> > -		if (ret && ret != -EIO)
> > +		if (ret)
> 
> Same here really.

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 875bdf814d73..1586d9107cba 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -13406,6 +13406,8 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
                        ret = __i915_wait_request(intel_plane_state->wait_req,
                                                  true, NULL, NULL);
                        if (ret) {
+                               /* Any hang should be swallowed by the wait */
+                               WARN_ON(ret == -EIO);
                                mutex_lock(&dev->struct_mutex);
                                drm_atomic_helper_cleanup_planes(dev, state);
                                mutex_unlock(&dev->struct_mutex);
@@ -13740,8 +13742,11 @@ intel_prepare_plane_fb(struct drm_plane *plane,
                 */
                if (needs_modeset(crtc_state))
                        ret = i915_gem_object_wait_rendering(old_obj, true);
-               if (ret)
+               if (ret) {
+                       /* GPU hangs should have been swallowed by the wait */
+                       WARN_ON(ret == -EIO);
                        return ret;
+               }
        }
 
        /* For framebuffer backed by dmabuf, wait for fence */



> We already have a WARN_ON in the mmio_flip, so are covered there already.
> 
> Otherwise looks good, and with the above addressed and under the
> assumption that the last caller of check_wedge is in request_alloc (which
> I was too lazy to check perfectly):

Yes, later it is moved to the new i915_gem_request.c and made static
alongside it's only caller request_alloc().
-Chris

-- 
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Re: [PATCH 09/32] drm/i915: Prevent leaking of -EIO from i915_wait_request()

[Daniel Vetter]

On Wed, Dec 16, 2015 at 11:06:20AM +0000, Chris Wilson wrote:
> On Wed, Dec 16, 2015 at 10:52:06AM +0100, Daniel Vetter wrote:
> > On Fri, Dec 11, 2015 at 11:33:05AM +0000, Chris Wilson wrote:
> > > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > > index d7bbd015de35..875bdf814d73 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -13405,10 +13405,6 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
> > >  
> > >  			ret = __i915_wait_request(intel_plane_state->wait_req,
> > >  						  true, NULL, NULL);
> > > -
> > > -			/* Swallow -EIO errors to allow updates during hw lockup. */
> > > -			if (ret == -EIO)
> > 
> > I'd like to keep a WARN_ON here since it's ABI relevant, and consistent
> > with the other places we've had a WARN_ON(-EIO).
> > 
> > > -				ret = 0;
> > >  			if (ret) {
> > >  				mutex_lock(&dev->struct_mutex);
> > >  				drm_atomic_helper_cleanup_planes(dev, state);
> > > @@ -13744,9 +13740,7 @@ intel_prepare_plane_fb(struct drm_plane *plane,
> > >  		 */
> > >  		if (needs_modeset(crtc_state))
> > >  			ret = i915_gem_object_wait_rendering(old_obj, true);
> > > -
> > > -		/* Swallow -EIO errors to allow updates during hw lockup. */
> > > -		if (ret && ret != -EIO)
> > > +		if (ret)
> > 
> > Same here really.
> 
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 875bdf814d73..1586d9107cba 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -13406,6 +13406,8 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
>                         ret = __i915_wait_request(intel_plane_state->wait_req,
>                                                   true, NULL, NULL);
>                         if (ret) {
> +                               /* Any hang should be swallowed by the wait */
> +                               WARN_ON(ret == -EIO);
>                                 mutex_lock(&dev->struct_mutex);
>                                 drm_atomic_helper_cleanup_planes(dev, state);
>                                 mutex_unlock(&dev->struct_mutex);
> @@ -13740,8 +13742,11 @@ intel_prepare_plane_fb(struct drm_plane *plane,
>                  */
>                 if (needs_modeset(crtc_state))
>                         ret = i915_gem_object_wait_rendering(old_obj, true);
> -               if (ret)
> +               if (ret) {
> +                       /* GPU hangs should have been swallowed by the wait */
> +                       WARN_ON(ret == -EIO);
>                         return ret;
> +               }
>         }
>  
>         /* For framebuffer backed by dmabuf, wait for fence */

lgtm.

> > We already have a WARN_ON in the mmio_flip, so are covered there already.
> > 
> > Otherwise looks good, and with the above addressed and under the
> > assumption that the last caller of check_wedge is in request_alloc (which
> > I was too lazy to check perfectly):
> 
> Yes, later it is moved to the new i915_gem_request.c and made static
> alongside it's only caller request_alloc().

Yeah, r-b confirmed ;-)
-Daniel
-- 
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[PATCH 10/32] drm/i915: Suppress error message when GPU resets are disabled

[Chris Wilson]

If we do not have lowlevel support for reseting the GPU, or if the user
has explicitly disabled reseting the device, the failure is expected.
Since it is an expected failure, we should be using a lower priority
message than *ERROR*, perhaps NOTICE. In the absence of DRM_NOTICE, just
emit the expected failure as a DEBUG message.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_drv.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 8bdc51bc00a4..ba91f65b6082 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -895,7 +895,10 @@ int i915_reset(struct drm_device *dev)
 		pr_notice("drm/i915: Resetting chip after gpu hang\n");
 
 	if (ret) {
-		DRM_ERROR("Failed to reset chip: %i\n", ret);
+		if (ret != -ENODEV)
+			DRM_ERROR("Failed to reset chip: %i\n", ret);
+		else
+			DRM_DEBUG_DRIVER("GPU reset disabled\n");
 		goto error;
 	}
 
-- 
2.6.3

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Re: [PATCH 10/32] drm/i915: Suppress error message when GPU resets are disabled

[Daniel Vetter]

On Fri, Dec 11, 2015 at 11:33:06AM +0000, Chris Wilson wrote:
> If we do not have lowlevel support for reseting the GPU, or if the user
> has explicitly disabled reseting the device, the failure is expected.
> Since it is an expected failure, we should be using a lower priority
> message than *ERROR*, perhaps NOTICE. In the absence of DRM_NOTICE, just
> emit the expected failure as a DEBUG message.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

lgtm. Are there now changes to gem_eio needed to adjust/improve test
coverage still? I lost a bit track on this part ...

I'll leave later patches to Mika&Tvrtko for detailed reviewing.
-Daniel

> ---
>  drivers/gpu/drm/i915/i915_drv.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 8bdc51bc00a4..ba91f65b6082 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -895,7 +895,10 @@ int i915_reset(struct drm_device *dev)
>  		pr_notice("drm/i915: Resetting chip after gpu hang\n");
>  
>  	if (ret) {
> -		DRM_ERROR("Failed to reset chip: %i\n", ret);
> +		if (ret != -ENODEV)
> +			DRM_ERROR("Failed to reset chip: %i\n", ret);
> +		else
> +			DRM_DEBUG_DRIVER("GPU reset disabled\n");
>  		goto error;
>  	}
>  
> -- 
> 2.6.3
> 

-- 
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Re: [PATCH 10/32] drm/i915: Suppress error message when GPU resets are disabled

[Chris Wilson]

On Wed, Dec 16, 2015 at 10:53:16AM +0100, Daniel Vetter wrote:
> On Fri, Dec 11, 2015 at 11:33:06AM +0000, Chris Wilson wrote:
> > If we do not have lowlevel support for reseting the GPU, or if the user
> > has explicitly disabled reseting the device, the failure is expected.
> > Since it is an expected failure, we should be using a lower priority
> > message than *ERROR*, perhaps NOTICE. In the absence of DRM_NOTICE, just
> > emit the expected failure as a DEBUG message.
> > 
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> 
> lgtm. Are there now changes to gem_eio needed to adjust/improve test
> coverage still? I lost a bit track on this part ...

The only remaining task for gem_eio (aside from adding more negative tests)
is to cement that wait-ioctl doesn't return EIO if it is wedged previously
or if a hang occurs during the wait.
-Chris

-- 
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[PATCH 11/32] drm/i915: Delay queuing hangcheck to wait-request

[Chris Wilson]

We can forgo queuing the hangcheck from the start of every request to
until we wait upon a request. This reduces the overhead of every
request, but may increase the latency of detecting a hang. Howeever, if
nothing every waits upon a hang, did it ever hang? It also improves the
robustness of the wait-request by ensuring that the hangchecker is
indeed running before we sleep indefinitely (and thereby ensuring that
we never actually sleep forever waiting for a dead GPU).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h | 2 +-
 drivers/gpu/drm/i915/i915_gem.c | 5 +++--
 drivers/gpu/drm/i915/i915_irq.c | 9 ++++-----
 3 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7acbc072973a..987a35c5af72 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2723,7 +2723,7 @@ void intel_hpd_cancel_work(struct drm_i915_private *dev_priv);
 bool intel_hpd_pin_to_port(enum hpd_pin pin, enum port *port);
 
 /* i915_irq.c */
-void i915_queue_hangcheck(struct drm_device *dev);
+void i915_queue_hangcheck(struct drm_i915_private *dev_priv);
 __printf(3, 4)
 void i915_handle_error(struct drm_device *dev, bool wedged,
 		       const char *fmt, ...);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f5760869a17c..0340a5fe9cda 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1308,6 +1308,9 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			break;
 		}
 
+		/* Ensure that even if the GPU hangs, we get woken up. */
+		i915_queue_hangcheck(dev_priv);
+
 		timer.function = NULL;
 		if (timeout || missed_irq(dev_priv, ring)) {
 			unsigned long expire;
@@ -2584,8 +2587,6 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 
 	trace_i915_gem_request_add(request);
 
-	i915_queue_hangcheck(ring->dev);
-
 	queue_delayed_work(dev_priv->wq,
 			   &dev_priv->mm.retire_work,
 			   round_jiffies_up_relative(HZ));
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 88206c0404d7..21089ac5dd58 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3066,15 +3066,14 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 	if (rings_hung)
 		return i915_handle_error(dev, true, "Ring hung");
 
+	/* Reset timer in case GPU hangs without another request being added */
 	if (busy_count)
-		/* Reset timer case chip hangs without another request
-		 * being added */
-		i915_queue_hangcheck(dev);
+		i915_queue_hangcheck(dev_priv);
 }
 
-void i915_queue_hangcheck(struct drm_device *dev)
+void i915_queue_hangcheck(struct drm_i915_private *dev_priv)
 {
-	struct i915_gpu_error *e = &to_i915(dev)->gpu_error;
+	struct i915_gpu_error *e = &dev_priv->gpu_error;
 
 	if (!i915.enable_hangcheck)
 		return;
-- 
2.6.3

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[PATCH 12/32] drm/i915: Remove the dedicated hangcheck workqueue

[Chris Wilson]

The queue only ever contains at most one item and has no special flags.
It is just a very simple wrapper around the system-wq - a complication
with no benefits.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c | 11 -----------
 drivers/gpu/drm/i915/i915_drv.h |  1 -
 drivers/gpu/drm/i915/i915_irq.c |  6 +++---
 3 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 84e2b202ecb5..1fdb52048cea 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1013,14 +1013,6 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 		goto out_freewq;
 	}
 
-	dev_priv->gpu_error.hangcheck_wq =
-		alloc_ordered_workqueue("i915-hangcheck", 0);
-	if (dev_priv->gpu_error.hangcheck_wq == NULL) {
-		DRM_ERROR("Failed to create our hangcheck workqueue.\n");
-		ret = -ENOMEM;
-		goto out_freedpwq;
-	}
-
 	intel_irq_init(dev_priv);
 	intel_uncore_sanitize(dev);
 
@@ -1100,8 +1092,6 @@ out_gem_unload:
 	intel_teardown_gmbus(dev);
 	intel_teardown_mchbar(dev);
 	pm_qos_remove_request(&dev_priv->pm_qos);
-	destroy_workqueue(dev_priv->gpu_error.hangcheck_wq);
-out_freedpwq:
 	destroy_workqueue(dev_priv->hotplug.dp_wq);
 out_freewq:
 	destroy_workqueue(dev_priv->wq);
@@ -1201,7 +1191,6 @@ int i915_driver_unload(struct drm_device *dev)
 
 	destroy_workqueue(dev_priv->hotplug.dp_wq);
 	destroy_workqueue(dev_priv->wq);
-	destroy_workqueue(dev_priv->gpu_error.hangcheck_wq);
 	pm_qos_remove_request(&dev_priv->pm_qos);
 
 	i915_global_gtt_cleanup(dev);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 987a35c5af72..9304ecfa05d4 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1333,7 +1333,6 @@ struct i915_gpu_error {
 	/* Hang gpu twice in this window and your context gets banned */
 #define DRM_I915_CTX_BAN_PERIOD DIV_ROUND_UP(8*DRM_I915_HANGCHECK_PERIOD, 1000)
 
-	struct workqueue_struct *hangcheck_wq;
 	struct delayed_work hangcheck_work;
 
 	/* For reset and error_state handling. */
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 21089ac5dd58..afe04aeb858d 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3073,7 +3073,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 void i915_queue_hangcheck(struct drm_i915_private *dev_priv)
 {
-	struct i915_gpu_error *e = &dev_priv->gpu_error;
+	unsigned long delay;
 
 	if (!i915.enable_hangcheck)
 		return;
@@ -3083,8 +3083,8 @@ void i915_queue_hangcheck(struct drm_i915_private *dev_priv)
 	 * we will ignore a hung ring if a second ring is kept busy.
 	 */
 
-	queue_delayed_work(e->hangcheck_wq, &e->hangcheck_work,
-			   round_jiffies_up_relative(DRM_I915_HANGCHECK_JIFFIES));
+	delay = round_jiffies_up_relative(DRM_I915_HANGCHECK_JIFFIES);
+	schedule_delayed_work(&dev_priv->gpu_error.hangcheck_work, delay);
 }
 
 static void ibx_irq_reset(struct drm_device *dev)
-- 
2.6.3

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[PATCH 13/32] drm/i915: Make queueing the hangcheck work inline

[Chris Wilson]

Since the function is a small wrapper around schedule_delayed_work(),
move it inline to remove the function call overhead for the principle
caller.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h | 17 ++++++++++++++++-
 drivers/gpu/drm/i915/i915_irq.c | 16 ----------------
 2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 9304ecfa05d4..f82e8fb19c9b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2722,7 +2722,22 @@ void intel_hpd_cancel_work(struct drm_i915_private *dev_priv);
 bool intel_hpd_pin_to_port(enum hpd_pin pin, enum port *port);
 
 /* i915_irq.c */
-void i915_queue_hangcheck(struct drm_i915_private *dev_priv);
+static inline void i915_queue_hangcheck(struct drm_i915_private *dev_priv)
+{
+	unsigned long delay;
+
+	if (unlikely(!i915.enable_hangcheck))
+		return;
+
+	/* Don't continually defer the hangcheck so that it is always run at
+	 * least once after work has been scheduled on any ring. Otherwise,
+	 * we will ignore a hung ring if a second ring is kept busy.
+	 */
+
+	delay = round_jiffies_up_relative(DRM_I915_HANGCHECK_JIFFIES);
+	schedule_delayed_work(&dev_priv->gpu_error.hangcheck_work, delay);
+}
+
 __printf(3, 4)
 void i915_handle_error(struct drm_device *dev, bool wedged,
 		       const char *fmt, ...);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index afe04aeb858d..5f88869e2207 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3071,22 +3071,6 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 		i915_queue_hangcheck(dev_priv);
 }
 
-void i915_queue_hangcheck(struct drm_i915_private *dev_priv)
-{
-	unsigned long delay;
-
-	if (!i915.enable_hangcheck)
-		return;
-
-	/* Don't continually defer the hangcheck so that it is always run at
-	 * least once after work has been scheduled on any ring. Otherwise,
-	 * we will ignore a hung ring if a second ring is kept busy.
-	 */
-
-	delay = round_jiffies_up_relative(DRM_I915_HANGCHECK_JIFFIES);
-	schedule_delayed_work(&dev_priv->gpu_error.hangcheck_work, delay);
-}
-
 static void ibx_irq_reset(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
-- 
2.6.3

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[PATCH 14/32] drm/i915: Remove forcewake dance from seqno/irq barrier on legacy gen6+

[Chris Wilson]

In order to ensure seqno/irq coherency, we current read a ring register.
We are not sure quite how it works, only that is does. Experiments show
that e.g. doing a clflush(seqno) instead is not sufficient, but we can
remove the forcewake dance from the mmio access.

v2: Baytrail wants a clflush too.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 6cecc15ec01b..69dd69e46fa9 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1490,10 +1490,21 @@ gen6_ring_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
 {
 	/* Workaround to force correct ordering between irq and seqno writes on
 	 * ivb (and maybe also on snb) by reading from a CS register (like
-	 * ACTHD) before reading the status page. */
+	 * ACTHD) before reading the status page.
+	 *
+	 * Note that this effectively effectively stalls the read by the time
+	 * it takes to do a memory transaction, which more or less ensures
+	 * that the write from the GPU has sufficient time to invalidate
+	 * the CPU cacheline. Alternatively we could delay the interrupt from
+	 * the CS ring to give the write time to land, but that would incur
+	 * a delay after every batch i.e. much more frequent than a delay
+	 * when waiting for the interrupt (with the same net latency).
+	 */
 	if (!lazy_coherency) {
 		struct drm_i915_private *dev_priv = ring->dev->dev_private;
-		POSTING_READ(RING_ACTHD(ring->mmio_base));
+		POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
+
+		intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 	}
 
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
-- 
2.6.3

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Re: [PATCH 14/32] drm/i915: Remove forcewake dance from seqno/irq barrier on legacy gen6+

[Dave Gordon]

On 11/12/15 11:33, Chris Wilson wrote:
> In order to ensure seqno/irq coherency, we current read a ring register.
> We are not sure quite how it works, only that is does. Experiments show
> that e.g. doing a clflush(seqno) instead is not sufficient, but we can
> remove the forcewake dance from the mmio access.
>
> v2: Baytrail wants a clflush too.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>   drivers/gpu/drm/i915/intel_ringbuffer.c | 15 +++++++++++++--
>   1 file changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 6cecc15ec01b..69dd69e46fa9 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -1490,10 +1490,21 @@ gen6_ring_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
>   {
>   	/* Workaround to force correct ordering between irq and seqno writes on
>   	 * ivb (and maybe also on snb) by reading from a CS register (like
> -	 * ACTHD) before reading the status page. */
> +	 * ACTHD) before reading the status page.
> +	 *
> +	 * Note that this effectively effectively stalls the read by the time
> +	 * it takes to do a memory transaction, which more or less ensures
> +	 * that the write from the GPU has sufficient time to invalidate
> +	 * the CPU cacheline. Alternatively we could delay the interrupt from
> +	 * the CS ring to give the write time to land, but that would incur
> +	 * a delay after every batch i.e. much more frequent than a delay
> +	 * when waiting for the interrupt (with the same net latency).
> +	 */
>   	if (!lazy_coherency) {
>   		struct drm_i915_private *dev_priv = ring->dev->dev_private;
> -		POSTING_READ(RING_ACTHD(ring->mmio_base));
> +		POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
> +
> +		intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
>   	}
>
>   	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);

Hmm ... would putting the flush before the POSTING_READ be better?

Depending on how the h/w implements the cacheline invalidation, it might 
allow some overlap between the cache controller's internal activities 
and the MMIO cycle ...

Also, previously we only had the flush on BXT, whereas now you're doing 
it on all gen6+. I think this is probably a good thing, but just 
wondered whether there's any downside to it?

Also ... are we sure that no-one calls this without having a forcewake 
in effect at the time, in particular debugfs? Or is it not going to end 
up going through here once lazy_coherency is abolished?

.Dave.
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[PATCH 15/32] drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

One particularly stressful scenario consists of many independent tasks
all competing for GPU time and waiting upon the results (e.g. realtime
transcoding of many, many streams). One bottleneck in particular is that
each client waits on its own results, but every client is woken up after
every batchbuffer - hence the thunder of hooves as then every client must
do its heavyweight dance to read a coherent seqno to see if it is the
lucky one.

Ideally, we only want one client to wake up after the interrupt and
check its request for completion. Since the requests must retire in
order, we can select the first client on the oldest request to be woken.
Once that client has completed his wait, we can then wake up the
next client and so on. However, all clients then incur latency as every
process in the chain may be delayed for scheduling - this may also then
cause some priority inversion. To reduce the latency, when a client
is added or removed from the list, we scan the tree for completed
seqno and wake up all the completed waiters in parallel.

v2: Convert from a kworker per engine into a dedicated kthread for the
bottom-half.
v3: Rename request members and tweak comments.
v4: Use a per-engine spinlock in the breadcrumbs bottom-half.
v5: Fix race in locklessly checking waiter status and kicking the task on
adding a new waiter.
v6: Fix deciding when to force the timer to hide missing interrupts.
v7: Move the bottom-half from the kthread to the first client process.
v8: Reword a few comments
v9: Break the busy loop when the interrupt is unmasked or has fired.
v10: Comments, unnecessary churn, better debugging from Tvrtko
v11: Wake all completed waiters on removing the current bottom-half to
reduce the latency of waking up a herd of clients all waiting on the
same request.
v12: Rearrange missed-interrupt fault injection so that it works with
igt/drv_missed_irq_hang

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
---
 drivers/gpu/drm/i915/Makefile            |   1 +
 drivers/gpu/drm/i915/i915_debugfs.c      |  19 ++-
 drivers/gpu/drm/i915/i915_drv.h          |   3 +-
 drivers/gpu/drm/i915/i915_gem.c          | 152 ++++++++---------
 drivers/gpu/drm/i915/i915_gpu_error.c    |   2 +-
 drivers/gpu/drm/i915/i915_irq.c          |  14 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 274 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c         |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c  |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  63 ++++++-
 10 files changed, 436 insertions(+), 102 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/intel_breadcrumbs.c

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 0851de07bd13..d3b9d3618719 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -35,6 +35,7 @@ i915-y += i915_cmd_parser.o \
 	  i915_gem_userptr.o \
 	  i915_gpu_error.o \
 	  i915_trace_points.o \
+	  intel_breadcrumbs.o \
 	  intel_lrc.o \
 	  intel_mocs.o \
 	  intel_ringbuffer.o \
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index d5f66bbdb160..48e574247a30 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -730,10 +730,22 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
 static void i915_ring_seqno_info(struct seq_file *m,
 				 struct intel_engine_cs *ring)
 {
+	struct rb_node *rb;
+
 	if (ring->get_seqno) {
 		seq_printf(m, "Current sequence (%s): %x\n",
 			   ring->name, ring->get_seqno(ring, false));
 	}
+
+	spin_lock(&ring->breadcrumbs.lock);
+	for (rb = rb_first(&ring->breadcrumbs.requests);
+	     rb != NULL;
+	     rb = rb_next(rb)) {
+		struct intel_breadcrumb *b = container_of(rb, typeof(*b), node);
+		seq_printf(m, "Waiting (%s): %s [%d] on %x\n",
+			   ring->name, b->task->comm, b->task->pid, b->seqno);
+	}
+	spin_unlock(&ring->breadcrumbs.lock);
 }
 
 static int i915_gem_seqno_info(struct seq_file *m, void *data)
@@ -1356,8 +1368,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 
 	for_each_ring(ring, dev_priv, i) {
 		seq_printf(m, "%s:\n", ring->name);
-		seq_printf(m, "\tseqno = %x [current %x]\n",
-			   ring->hangcheck.seqno, seqno[i]);
+		seq_printf(m, "\tseqno = %x [current %x], waiters? %d\n",
+			   ring->hangcheck.seqno, seqno[i],
+			   intel_engine_has_waiter(ring));
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
 			   (long long)acthd[i]);
@@ -2322,7 +2335,7 @@ static int count_irq_waiters(struct drm_i915_private *i915)
 	int i;
 
 	for_each_ring(ring, i915, i)
-		count += ring->irq_refcount;
+		count += intel_engine_has_waiter(ring);
 
 	return count;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index f82e8fb19c9b..830d760aa562 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1382,7 +1382,7 @@ struct i915_gpu_error {
 #define I915_STOP_RING_ALLOW_WARN      (1 << 30)
 
 	/* For missed irq/seqno simulation. */
-	unsigned int test_irq_rings;
+	unsigned long test_irq_rings;
 };
 
 enum modeset_restore {
@@ -2825,7 +2825,6 @@ ibx_disable_display_interrupt(struct drm_i915_private *dev_priv, uint32_t bits)
 	ibx_display_interrupt_update(dev_priv, bits, 0);
 }
 
-
 /* i915_gem.c */
 int i915_gem_create_ioctl(struct drm_device *dev, void *data,
 			  struct drm_file *file_priv);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 0340a5fe9cda..fa0cf6c9f4d0 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1123,17 +1123,6 @@ i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
 	return 0;
 }
 
-static void fake_irq(unsigned long data)
-{
-	wake_up_process((struct task_struct *)data);
-}
-
-static bool missed_irq(struct drm_i915_private *dev_priv,
-		       struct intel_engine_cs *ring)
-{
-	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
-}
-
 static unsigned long local_clock_us(unsigned *cpu)
 {
 	unsigned long t;
@@ -1166,7 +1155,9 @@ static bool busywait_stop(unsigned long timeout, unsigned cpu)
 	return this_cpu != cpu;
 }
 
-static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
+static bool __i915_spin_request(struct drm_i915_gem_request *req,
+				struct intel_breadcrumb *wait,
+				int state)
 {
 	unsigned long timeout;
 	unsigned cpu;
@@ -1181,31 +1172,30 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 	 * takes to sleep on a request, on the order of a microsecond.
 	 */
 
-	if (req->ring->irq_refcount)
-		return -EBUSY;
-
 	/* Only spin if we know the GPU is processing this request */
 	if (!i915_gem_request_started(req, true))
-		return -EAGAIN;
+		return false;
 
 	timeout = local_clock_us(&cpu) + 5;
-	while (!need_resched()) {
+	do {
 		if (i915_gem_request_completed(req, true))
-			return 0;
+			return true;
 
-		if (signal_pending_state(state, current))
+		if (signal_pending_state(state, wait->task))
 			break;
 
 		if (busywait_stop(timeout, cpu))
 			break;
 
 		cpu_relax_lowlatency();
-	}
 
-	if (i915_gem_request_completed(req, false))
-		return 0;
+		/* Break the loop if we have consumed the timeslice (or been
+		 * preempted) or when either the background thread has
+		 * enabled the interrupt, or the IRQ has fired.
+		 */
+	} while (!need_resched() && wait->task->state == state);
 
-	return -EAGAIN;
+	return false;
 }
 
 /**
@@ -1229,18 +1219,13 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			s64 *timeout,
 			struct intel_rps_client *rps)
 {
-	struct intel_engine_cs *ring = i915_gem_request_get_ring(req);
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	const bool irq_test_in_progress =
-		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
 	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
-	DEFINE_WAIT(wait);
-	unsigned long timeout_expire;
+	struct intel_breadcrumb wait;
+	unsigned long timeout_remain;
 	s64 before, now;
-	int ret;
+	int ret = 0;
 
-	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
+	might_sleep();
 
 	if (list_empty(&req->list))
 		return 0;
@@ -1248,7 +1233,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	if (i915_gem_request_completed(req, true))
 		return 0;
 
-	timeout_expire = 0;
+	timeout_remain = MAX_SCHEDULE_TIMEOUT;
 	if (timeout) {
 		if (WARN_ON(*timeout < 0))
 			return -EINVAL;
@@ -1256,83 +1241,80 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 		if (*timeout == 0)
 			return -ETIME;
 
-		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
+		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
 	}
 
-	if (INTEL_INFO(dev_priv)->gen >= 6)
-		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
-
 	/* Record current time in case interrupted by signal, or wedged */
 	trace_i915_gem_request_wait_begin(req);
 	before = ktime_get_raw_ns();
 
-	/* Optimistic spin for the next jiffie before touching IRQs */
-	ret = __i915_spin_request(req, state);
-	if (ret == 0)
-		goto out;
+	if (INTEL_INFO(req->i915)->gen >= 6)
+		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
-	if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) {
-		ret = -ENODEV;
-		goto out;
-	}
+	intel_breadcrumb_init(&wait, req->seqno);
+	set_task_state(wait.task, state);
 
-	for (;;) {
-		struct timer_list timer;
+	/* Optimistic spin for the next ~jiffie before touching IRQs */
+	if (intel_engine_add_breadcrumb(req->ring, &wait)) {
+		if (__i915_spin_request(req, &wait, state))
+			goto out;
 
-		prepare_to_wait(&ring->irq_queue, &wait, state);
+		intel_engine_enable_breadcrumb_irq(req->ring);
 
-		/* We need to check whether any gpu reset happened in between
-		 * the request being submitted and now. If a reset has occurred,
-		 * the request is effectively complete (we either are in the
-		 * process of or have discarded the rendering and completely
-		 * reset the GPU. The results of the request are lost and we
-		 * are free to continue on with the original operation.
+		/* In order to check that we haven't missed the interrupt
+		 * as we enabled it, we need to kick ourselves to do a
+		 * coherent check on the seqno before we sleep.
 		 */
-		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
-			ret = 0;
-			break;
-		}
-
-		if (i915_gem_request_completed(req, false)) {
-			ret = 0;
-			break;
-		}
+		goto wakeup;
+	}
 
-		if (signal_pending_state(state, current)) {
+	for (;;) {
+		if (signal_pending_state(state, wait.task)) {
 			ret = -ERESTARTSYS;
 			break;
 		}
 
-		if (timeout && time_after_eq(jiffies, timeout_expire)) {
+		/* Ensure that even if the GPU hangs, we get woken up. */
+		i915_queue_hangcheck(req->i915);
+
+		timeout_remain = io_schedule_timeout(timeout_remain);
+		if (timeout_remain == 0) {
 			ret = -ETIME;
 			break;
 		}
 
-		/* Ensure that even if the GPU hangs, we get woken up. */
-		i915_queue_hangcheck(dev_priv);
-
-		timer.function = NULL;
-		if (timeout || missed_irq(dev_priv, ring)) {
-			unsigned long expire;
+		if (intel_breadcrumb_complete(&wait))
+			break;
 
-			setup_timer_on_stack(&timer, fake_irq, (unsigned long)current);
-			expire = missed_irq(dev_priv, ring) ? jiffies + 1 : timeout_expire;
-			mod_timer(&timer, expire);
-		}
+wakeup:		set_task_state(wait.task, state);
 
-		io_schedule();
+		/* Ensure our read of the seqno is coherent so that we
+		 * do not "miss an interrupt" (i.e. if this is the last
+		 * request and the seqno write from the GPU is not visible
+		 * by the time the interrupt fires, we will see that the
+		 * request is incomplete and go back to sleep awaiting
+		 * another interrupt that will never come.)
+		 *
+		 * Strictly, we only need to do this once after an interrupt,
+		 * but it is easier and safer to do it every time the waiter
+		 * is woken.
+		 */
+		if (i915_gem_request_completed(req, false))
+			break;
 
-		if (timer.function) {
-			del_singleshot_timer_sync(&timer);
-			destroy_timer_on_stack(&timer);
-		}
+		/* We need to check whether any gpu reset happened in between
+		 * the request being submitted and now. If a reset has occurred,
+		 * the request is effectively complete (we either are in the
+		 * process of or have discarded the rendering and completely
+		 * reset the GPU. The results of the request are lost and we
+		 * are free to continue on with the original operation.
+		 */
+		if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
+			break;
 	}
-	if (!irq_test_in_progress)
-		ring->irq_put(ring);
-
-	finish_wait(&ring->irq_queue, &wait);
-
 out:
+	intel_engine_remove_breadcrumb(req->ring, &wait);
+	__set_task_state(wait.task, TASK_RUNNING);
 	now = ktime_get_raw_ns();
 	trace_i915_gem_request_wait_end(req);
 
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 06ca4082735b..f805d117f3d1 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -900,7 +900,7 @@ static void i915_record_ring_state(struct drm_device *dev,
 		ering->instdone = I915_READ(GEN2_INSTDONE);
 	}
 
-	ering->waiting = waitqueue_active(&ring->irq_queue);
+	ering->waiting = intel_engine_has_waiter(ring);
 	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
 	ering->seqno = ring->get_seqno(ring, false);
 	ering->acthd = intel_ring_get_active_head(ring);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 5f88869e2207..d250b4721a6a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1000,8 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
 		return;
 
 	trace_i915_gem_request_notify(ring);
-
-	wake_up_all(&ring->irq_queue);
+	intel_engine_wakeup(ring);
 }
 
 static void vlv_c0_read(struct drm_i915_private *dev_priv,
@@ -1083,7 +1082,7 @@ static bool any_waiters(struct drm_i915_private *dev_priv)
 	int i;
 
 	for_each_ring(ring, dev_priv, i)
-		if (ring->irq_refcount)
+		if (intel_engine_has_waiter(ring))
 			return true;
 
 	return false;
@@ -2411,7 +2410,7 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 
 	/* Wake up __wait_seqno, potentially holding dev->struct_mutex. */
 	for_each_ring(ring, dev_priv, i)
-		wake_up_all(&ring->irq_queue);
+		intel_engine_wakeup(ring);
 
 	/* Wake up intel_crtc_wait_for_pending_flips, holding crtc->mutex. */
 	wake_up_all(&dev_priv->pending_flip_queue);
@@ -2986,16 +2985,17 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 			if (ring_idle(ring, seqno)) {
 				ring->hangcheck.action = HANGCHECK_IDLE;
 
-				if (waitqueue_active(&ring->irq_queue)) {
+				if (intel_engine_has_waiter(ring)) {
 					/* Issue a wake-up to catch stuck h/w. */
 					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
-						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
+						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
 						else
 							DRM_INFO("Fake missed irq on %s\n",
 								 ring->name);
-						wake_up_all(&ring->irq_queue);
+
+						intel_engine_enable_fake_irq(ring);
 					}
 					/* Safeguard against driver failure */
 					ring->hangcheck.score += BUSY;
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
new file mode 100644
index 000000000000..a9a199bca2c2
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -0,0 +1,274 @@
+/*
+ * Copyright © 2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+
+static void intel_breadcrumbs_fake_irq(unsigned long data)
+{
+	struct intel_breadcrumbs *b = (struct intel_breadcrumbs *)data;
+	struct task_struct *task;
+
+	/*
+	 * The timer persists in case we cannot enable interrupts,
+	 * or if we have previously seen seqno/interrupt incoherency
+	 * ("missed interrupt" syndrome). Here the worker will wake up
+	 * every jiffie in order to kick the oldest waiter to do the
+	 * coherent seqno check.
+	 */
+
+	task = READ_ONCE(b->first_waiter);
+	if (task) {
+		wake_up_process(task);
+		mod_timer(&b->fake_irq, jiffies + 1);
+	}
+}
+
+static void irq_enable(struct intel_engine_cs *engine)
+{
+	WARN_ON(!engine->irq_get(engine));
+}
+
+static void irq_disable(struct intel_engine_cs *engine)
+{
+	engine->irq_put(engine);
+}
+
+static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+	bool noirq;
+
+	if (b->rpm_wakelock)
+		return;
+
+	/* Since we are waiting on a request, the GPU should be busy
+	 * and should have its own rpm reference. For completeness,
+	 * record an rpm reference for ourselves to cover the
+	 * interrupt we unmask.
+	 */
+	intel_runtime_pm_get_noresume(engine->i915);
+	b->rpm_wakelock = true;
+
+	/* No interrupts? Kick the waiter every jiffie! */
+	noirq = true;
+	if (intel_irqs_enabled(engine->i915)) {
+		noirq = test_bit(engine->id,
+				 &engine->i915->gpu_error.missed_irq_rings);
+		if (!test_bit(engine->id,
+			      &engine->i915->gpu_error.test_irq_rings)) {
+			irq_enable(engine);
+			b->irq_enabled = true;
+		}
+	}
+	if (noirq)
+		mod_timer(&b->fake_irq, jiffies + 1);
+}
+
+static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+
+	if (!b->rpm_wakelock)
+		return;
+
+	if (b->irq_enabled) {
+		irq_disable(engine);
+		b->irq_enabled = false;
+	}
+
+	intel_runtime_pm_put(engine->i915);
+	b->rpm_wakelock = false;
+}
+
+inline struct intel_breadcrumb *to_crumb(struct rb_node *node)
+{
+	return container_of(node, struct intel_breadcrumb, node);
+}
+
+bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
+				 struct intel_breadcrumb *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	u32 seqno = engine->get_seqno(engine, true);
+	struct rb_node **p, *parent, *completed;
+	bool first;
+
+	spin_lock(&b->lock);
+
+	/* Insert the request into the retirment ordered list
+	 * of waiters by walking the rbtree. If we are the oldest
+	 * seqno in the tree (the first to be retired), then
+	 * set ourselves as the bottom-half.
+	 *
+	 * As we descend the tree, prune completed branches since we hold the
+	 * spinlock we know that the first_waiter must be delayed and can
+	 * reduce some of the sequential wake up latency if we take action
+	 * ourselves and wake up the copmleted tasks in parallel.
+	 */
+	first = true;
+	parent = NULL;
+	completed = NULL;
+	p = &b->requests.rb_node;
+	while (*p) {
+		parent = *p;
+		if (i915_seqno_passed(wait->seqno, to_crumb(parent)->seqno)) {
+			p = &parent->rb_right;
+			if (i915_seqno_passed(seqno, to_crumb(parent)->seqno))
+				completed = parent;
+			else
+				first = false;
+		} else
+			p = &parent->rb_left;
+	}
+	rb_link_node(&wait->node, parent, p);
+	rb_insert_color(&wait->node, &b->requests);
+
+	if (completed != NULL) {
+		struct rb_node *next = rb_next(completed);
+
+		if (next && next != &wait->node) {
+			smp_store_mb(b->first_waiter, to_crumb(next)->task);
+			__intel_breadcrumbs_enable_irq(b);
+			wake_up_process(to_crumb(next)->task);
+		}
+
+		do {
+			struct intel_breadcrumb *crumb = to_crumb(completed);
+			completed = rb_prev(completed);
+
+			rb_erase(&crumb->node, &b->requests);
+			RB_CLEAR_NODE(&crumb->node);
+			wake_up_process(crumb->task);
+		} while (completed != NULL);
+	}
+
+	if (first)
+		smp_store_mb(b->first_waiter, wait->task);
+	BUG_ON(b->first_waiter == NULL);
+
+	spin_unlock(&b->lock);
+
+	return first;
+}
+
+void intel_engine_enable_breadcrumb_irq(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock(&b->lock);
+	__intel_breadcrumbs_enable_irq(b);
+	spin_unlock(&b->lock);
+}
+
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
+{
+	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+}
+
+void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
+				    struct intel_breadcrumb *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	/* Quick check to see if this waiter was already decoupled from
+	 * the tree by the bottom-half to avoid contention on the spinlock
+	 * by the herd.
+	 */
+	if (RB_EMPTY_NODE(&wait->node))
+		return;
+
+	spin_lock(&b->lock);
+
+	if (b->first_waiter == wait->task) {
+		struct rb_node *next;
+		struct task_struct *task;
+
+		/* We are the current bottom-half. Find the next candidate,
+		 * the first waiter in the queue on the remaining oldest
+		 * request. As multiple seqnos may complete in the time it
+		 * takes us to wake up and find the next waiter, we have to
+		 * wake up that waiter for it to perform its own coherent
+		 * completion check.
+		 */
+		next = rb_next(&wait->node);
+		if (next) {
+			/* If the next waiter is already complete,
+			 * wake it up and continue onto the next waiter. So
+			 * if have a small herd, they will wake up in parallel
+			 * rather than sequentially, which should reduce
+			 * the overall latency in waking all the completed
+			 * clients.
+			 */
+			u32 seqno = engine->get_seqno(engine, true);
+			while (i915_seqno_passed(seqno,
+						 to_crumb(next)->seqno)) {
+				struct rb_node *n = rb_next(next);
+
+				rb_erase(next, &b->requests);
+				RB_CLEAR_NODE(next);
+				wake_up_process(to_crumb(next)->task);
+
+				next = n;
+				if (next == NULL)
+					break;
+			}
+		}
+		task = next ? to_crumb(next)->task : NULL;
+
+		smp_store_mb(b->first_waiter, task);
+		if (task) {
+			/* In our haste, we may have completed the first waiter
+			 * before we enabled the interrupt. Do so now as we
+			 * have a second waiter for a future seqno. Afterwards,
+			 * we have to wake up that waiter in case we missed
+			 * the interrupt, or if we have to handle an
+			 * exception rather than a seqno completion.
+			 */
+			__intel_breadcrumbs_enable_irq(b);
+			wake_up_process(task);
+		} else
+			__intel_breadcrumbs_disable_irq(b);
+	}
+
+	if (!RB_EMPTY_NODE(&wait->node))
+		rb_erase(&wait->node, &b->requests);
+	spin_unlock(&b->lock);
+}
+
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock_init(&b->lock);
+	setup_timer(&b->fake_irq, intel_breadcrumbs_fake_irq, (unsigned long)b);
+}
+
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	del_timer_sync(&b->fake_irq);
+}
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 7030ff526941..780aa6d390aa 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1898,6 +1898,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
 
+	intel_engine_fini_breadcrumbs(ring);
+
 	if (ring->status_page.obj) {
 		kunmap(sg_page(ring->status_page.obj->pages->sgl));
 		ring->status_page.obj = NULL;
@@ -1915,10 +1917,11 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
 	ring->buffer = NULL;
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	INIT_LIST_HEAD(&ring->buffers);
 	INIT_LIST_HEAD(&ring->execlist_queue);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 69dd69e46fa9..e90c28e2da31 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2152,6 +2152,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	WARN_ON(ring->buffer);
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	INIT_LIST_HEAD(&ring->execlist_queue);
@@ -2159,7 +2160,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
 	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
 
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	ringbuf = intel_engine_create_ringbuffer(ring, 32 * PAGE_SIZE);
 	if (IS_ERR(ringbuf)) {
@@ -2223,6 +2224,8 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring)
 
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
+	intel_engine_fini_breadcrumbs(ring);
+
 	ring->dev = NULL;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 49574ffe54bc..281ed2c92b91 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -157,9 +157,35 @@ struct  intel_engine_cs {
 #define LAST_USER_RING (VECS + 1)
 	u32		mmio_base;
 	struct		drm_device *dev;
+	struct drm_i915_private *i915;
 	struct intel_ringbuffer *buffer;
 	struct list_head buffers;
 
+	/* Rather than have every client wait upon all user interrupts,
+	 * with the herd waking after every interrupt and each doing the
+	 * heavyweight seqno dance, we delegate the task (of being the
+	 * bottom-half of the user interrupt) to the first client. After
+	 * every interrupt, we wake up one client, who does the heavyweight
+	 * coherent seqno read and either goes back to sleep (if incomplete),
+	 * or wakes up all the completed clients in parallel, before then
+	 * transferring the bottom-half status to the next client in the queue.
+	 *
+	 * Compared to walking the entire list of waiters in a single dedicated
+	 * bottom-half, we reduce the latency of the first waiter by avoiding
+	 * a context switch, but incur additional coherent seqno reads when
+	 * following the chain of request breadcrumbs. Since it is most likely
+	 * that we have a single client waiting on each seqno, then reducing
+	 * the overhead of waking that client is much preferred.
+	 */
+	struct intel_breadcrumbs {
+		spinlock_t lock; /* protects the lists of requests */
+		struct rb_root requests; /* sorted by retirement */
+		struct task_struct *first_waiter; /* bh for user interrupts */
+		struct timer_list fake_irq; /* used after a missed interrupt */
+		bool irq_enabled;
+		bool rpm_wakelock;
+	} breadcrumbs;
+
 	/*
 	 * A pool of objects to use as shadow copies of client batch buffers
 	 * when the command parser is enabled. Prevents the client from
@@ -303,8 +329,6 @@ struct  intel_engine_cs {
 
 	bool gpu_caches_dirty;
 
-	wait_queue_head_t irq_queue;
-
 	struct intel_context *default_context;
 	struct intel_context *last_context;
 
@@ -510,4 +534,39 @@ void intel_ring_reserved_space_end(struct intel_ringbuffer *ringbuf);
 /* Legacy ringbuffer specific portion of reservation code: */
 int intel_ring_reserve_space(struct drm_i915_gem_request *request);
 
+/* intel_breadcrumbs.c -- user interrupt bottom-half for waiters */
+struct intel_breadcrumb {
+	struct rb_node node;
+	struct task_struct *task;
+	u32 seqno;
+};
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine);
+static inline void intel_breadcrumb_init(struct intel_breadcrumb *wait,
+					 u32 seqno)
+{
+	wait->task = current;
+	wait->seqno = seqno;
+}
+static inline bool intel_breadcrumb_complete(struct intel_breadcrumb *wait)
+{
+	return RB_EMPTY_NODE(&wait->node);
+}
+bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
+				 struct intel_breadcrumb *wait);
+void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
+				    struct intel_breadcrumb *wait);
+static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
+{
+	return READ_ONCE(engine->breadcrumbs.first_waiter);
+}
+static inline void intel_engine_wakeup(struct intel_engine_cs *engine)
+{
+	struct task_struct *task = READ_ONCE(engine->breadcrumbs.first_waiter);
+	if (task)
+		wake_up_process(task);
+}
+void intel_engine_enable_breadcrumb_irq(struct intel_engine_cs *engine);
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine);
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
+
 #endif /* _INTEL_RINGBUFFER_H_ */
-- 
2.6.3

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

Re: [PATCH 15/32] drm/i915: Slaughter the thundering i915_wait_request herd

[Tvrtko Ursulin]

Hi,

On 11/12/15 11:33, Chris Wilson wrote:
> One particularly stressful scenario consists of many independent tasks
> all competing for GPU time and waiting upon the results (e.g. realtime
> transcoding of many, many streams). One bottleneck in particular is that
> each client waits on its own results, but every client is woken up after
> every batchbuffer - hence the thunder of hooves as then every client must
> do its heavyweight dance to read a coherent seqno to see if it is the
> lucky one.
>
> Ideally, we only want one client to wake up after the interrupt and
> check its request for completion. Since the requests must retire in
> order, we can select the first client on the oldest request to be woken.
> Once that client has completed his wait, we can then wake up the
> next client and so on. However, all clients then incur latency as every
> process in the chain may be delayed for scheduling - this may also then
> cause some priority inversion. To reduce the latency, when a client
> is added or removed from the list, we scan the tree for completed
> seqno and wake up all the completed waiters in parallel.
>
> v2: Convert from a kworker per engine into a dedicated kthread for the
> bottom-half.
> v3: Rename request members and tweak comments.
> v4: Use a per-engine spinlock in the breadcrumbs bottom-half.
> v5: Fix race in locklessly checking waiter status and kicking the task on
> adding a new waiter.
> v6: Fix deciding when to force the timer to hide missing interrupts.
> v7: Move the bottom-half from the kthread to the first client process.
> v8: Reword a few comments
> v9: Break the busy loop when the interrupt is unmasked or has fired.
> v10: Comments, unnecessary churn, better debugging from Tvrtko
> v11: Wake all completed waiters on removing the current bottom-half to
> reduce the latency of waking up a herd of clients all waiting on the
> same request.
> v12: Rearrange missed-interrupt fault injection so that it works with
> igt/drv_missed_irq_hang
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
> Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> Cc: Dave Gordon <david.s.gordon@intel.com>
> ---
>   drivers/gpu/drm/i915/Makefile            |   1 +
>   drivers/gpu/drm/i915/i915_debugfs.c      |  19 ++-
>   drivers/gpu/drm/i915/i915_drv.h          |   3 +-
>   drivers/gpu/drm/i915/i915_gem.c          | 152 ++++++++---------
>   drivers/gpu/drm/i915/i915_gpu_error.c    |   2 +-
>   drivers/gpu/drm/i915/i915_irq.c          |  14 +-
>   drivers/gpu/drm/i915/intel_breadcrumbs.c | 274 +++++++++++++++++++++++++++++++
>   drivers/gpu/drm/i915/intel_lrc.c         |   5 +-
>   drivers/gpu/drm/i915/intel_ringbuffer.c  |   5 +-
>   drivers/gpu/drm/i915/intel_ringbuffer.h  |  63 ++++++-
>   10 files changed, 436 insertions(+), 102 deletions(-)
>   create mode 100644 drivers/gpu/drm/i915/intel_breadcrumbs.c
>
> diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
> index 0851de07bd13..d3b9d3618719 100644
> --- a/drivers/gpu/drm/i915/Makefile
> +++ b/drivers/gpu/drm/i915/Makefile
> @@ -35,6 +35,7 @@ i915-y += i915_cmd_parser.o \
>   	  i915_gem_userptr.o \
>   	  i915_gpu_error.o \
>   	  i915_trace_points.o \
> +	  intel_breadcrumbs.o \
>   	  intel_lrc.o \
>   	  intel_mocs.o \
>   	  intel_ringbuffer.o \
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index d5f66bbdb160..48e574247a30 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -730,10 +730,22 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
>   static void i915_ring_seqno_info(struct seq_file *m,
>   				 struct intel_engine_cs *ring)
>   {
> +	struct rb_node *rb;
> +
>   	if (ring->get_seqno) {
>   		seq_printf(m, "Current sequence (%s): %x\n",
>   			   ring->name, ring->get_seqno(ring, false));
>   	}
> +
> +	spin_lock(&ring->breadcrumbs.lock);
> +	for (rb = rb_first(&ring->breadcrumbs.requests);
> +	     rb != NULL;
> +	     rb = rb_next(rb)) {
> +		struct intel_breadcrumb *b = container_of(rb, typeof(*b), node);
> +		seq_printf(m, "Waiting (%s): %s [%d] on %x\n",
> +			   ring->name, b->task->comm, b->task->pid, b->seqno);
> +	}
> +	spin_unlock(&ring->breadcrumbs.lock);
>   }
>
>   static int i915_gem_seqno_info(struct seq_file *m, void *data)
> @@ -1356,8 +1368,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
>
>   	for_each_ring(ring, dev_priv, i) {
>   		seq_printf(m, "%s:\n", ring->name);
> -		seq_printf(m, "\tseqno = %x [current %x]\n",
> -			   ring->hangcheck.seqno, seqno[i]);
> +		seq_printf(m, "\tseqno = %x [current %x], waiters? %d\n",
> +			   ring->hangcheck.seqno, seqno[i],
> +			   intel_engine_has_waiter(ring));
>   		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
>   			   (long long)ring->hangcheck.acthd,
>   			   (long long)acthd[i]);
> @@ -2322,7 +2335,7 @@ static int count_irq_waiters(struct drm_i915_private *i915)
>   	int i;
>
>   	for_each_ring(ring, i915, i)
> -		count += ring->irq_refcount;
> +		count += intel_engine_has_waiter(ring);
>
>   	return count;
>   }
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index f82e8fb19c9b..830d760aa562 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -1382,7 +1382,7 @@ struct i915_gpu_error {
>   #define I915_STOP_RING_ALLOW_WARN      (1 << 30)
>
>   	/* For missed irq/seqno simulation. */
> -	unsigned int test_irq_rings;
> +	unsigned long test_irq_rings;
>   };
>
>   enum modeset_restore {
> @@ -2825,7 +2825,6 @@ ibx_disable_display_interrupt(struct drm_i915_private *dev_priv, uint32_t bits)
>   	ibx_display_interrupt_update(dev_priv, bits, 0);
>   }
>
> -
>   /* i915_gem.c */
>   int i915_gem_create_ioctl(struct drm_device *dev, void *data,
>   			  struct drm_file *file_priv);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 0340a5fe9cda..fa0cf6c9f4d0 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1123,17 +1123,6 @@ i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
>   	return 0;
>   }
>
> -static void fake_irq(unsigned long data)
> -{
> -	wake_up_process((struct task_struct *)data);
> -}
> -
> -static bool missed_irq(struct drm_i915_private *dev_priv,
> -		       struct intel_engine_cs *ring)
> -{
> -	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
> -}
> -
>   static unsigned long local_clock_us(unsigned *cpu)
>   {
>   	unsigned long t;
> @@ -1166,7 +1155,9 @@ static bool busywait_stop(unsigned long timeout, unsigned cpu)
>   	return this_cpu != cpu;
>   }
>
> -static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
> +static bool __i915_spin_request(struct drm_i915_gem_request *req,
> +				struct intel_breadcrumb *wait,
> +				int state)
>   {
>   	unsigned long timeout;
>   	unsigned cpu;
> @@ -1181,31 +1172,30 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
>   	 * takes to sleep on a request, on the order of a microsecond.
>   	 */
>
> -	if (req->ring->irq_refcount)
> -		return -EBUSY;
> -
>   	/* Only spin if we know the GPU is processing this request */
>   	if (!i915_gem_request_started(req, true))
> -		return -EAGAIN;
> +		return false;
>
>   	timeout = local_clock_us(&cpu) + 5;
> -	while (!need_resched()) {
> +	do {
>   		if (i915_gem_request_completed(req, true))
> -			return 0;
> +			return true;
>
> -		if (signal_pending_state(state, current))
> +		if (signal_pending_state(state, wait->task))
>   			break;
>
>   		if (busywait_stop(timeout, cpu))
>   			break;
>
>   		cpu_relax_lowlatency();
> -	}
>
> -	if (i915_gem_request_completed(req, false))
> -		return 0;
> +		/* Break the loop if we have consumed the timeslice (or been
> +		 * preempted) or when either the background thread has
> +		 * enabled the interrupt, or the IRQ has fired.
> +		 */
> +	} while (!need_resched() && wait->task->state == state);
>
> -	return -EAGAIN;
> +	return false;
>   }
>
>   /**
> @@ -1229,18 +1219,13 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>   			s64 *timeout,
>   			struct intel_rps_client *rps)
>   {
> -	struct intel_engine_cs *ring = i915_gem_request_get_ring(req);
> -	struct drm_device *dev = ring->dev;
> -	struct drm_i915_private *dev_priv = dev->dev_private;
> -	const bool irq_test_in_progress =
> -		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
>   	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
> -	DEFINE_WAIT(wait);
> -	unsigned long timeout_expire;
> +	struct intel_breadcrumb wait;
> +	unsigned long timeout_remain;
>   	s64 before, now;
> -	int ret;
> +	int ret = 0;
>
> -	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
> +	might_sleep();

Why this suddenly?

>
>   	if (list_empty(&req->list))
>   		return 0;
> @@ -1248,7 +1233,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>   	if (i915_gem_request_completed(req, true))
>   		return 0;
>
> -	timeout_expire = 0;
> +	timeout_remain = MAX_SCHEDULE_TIMEOUT;
>   	if (timeout) {
>   		if (WARN_ON(*timeout < 0))
>   			return -EINVAL;
> @@ -1256,83 +1241,80 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>   		if (*timeout == 0)
>   			return -ETIME;
>
> -		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
> +		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
>   	}
>
> -	if (INTEL_INFO(dev_priv)->gen >= 6)
> -		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
> -
>   	/* Record current time in case interrupted by signal, or wedged */
>   	trace_i915_gem_request_wait_begin(req);
>   	before = ktime_get_raw_ns();
>
> -	/* Optimistic spin for the next jiffie before touching IRQs */
> -	ret = __i915_spin_request(req, state);
> -	if (ret == 0)
> -		goto out;
> +	if (INTEL_INFO(req->i915)->gen >= 6)
> +		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
>
> -	if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) {
> -		ret = -ENODEV;
> -		goto out;
> -	}
> +	intel_breadcrumb_init(&wait, req->seqno);
> +	set_task_state(wait.task, state);
>
> -	for (;;) {
> -		struct timer_list timer;
> +	/* Optimistic spin for the next ~jiffie before touching IRQs */
> +	if (intel_engine_add_breadcrumb(req->ring, &wait)) {
> +		if (__i915_spin_request(req, &wait, state))
> +			goto out;
>
> -		prepare_to_wait(&ring->irq_queue, &wait, state);
> +		intel_engine_enable_breadcrumb_irq(req->ring);
>
> -		/* We need to check whether any gpu reset happened in between
> -		 * the request being submitted and now. If a reset has occurred,
> -		 * the request is effectively complete (we either are in the
> -		 * process of or have discarded the rendering and completely
> -		 * reset the GPU. The results of the request are lost and we
> -		 * are free to continue on with the original operation.
> +		/* In order to check that we haven't missed the interrupt
> +		 * as we enabled it, we need to kick ourselves to do a
> +		 * coherent check on the seqno before we sleep.
>   		 */
> -		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
> -			ret = 0;
> -			break;
> -		}
> -
> -		if (i915_gem_request_completed(req, false)) {
> -			ret = 0;
> -			break;
> -		}
> +		goto wakeup;
> +	}
>
> -		if (signal_pending_state(state, current)) {
> +	for (;;) {
> +		if (signal_pending_state(state, wait.task)) {
>   			ret = -ERESTARTSYS;
>   			break;
>   		}
>
> -		if (timeout && time_after_eq(jiffies, timeout_expire)) {
> +		/* Ensure that even if the GPU hangs, we get woken up. */
> +		i915_queue_hangcheck(req->i915);
> +
> +		timeout_remain = io_schedule_timeout(timeout_remain);
> +		if (timeout_remain == 0) {
>   			ret = -ETIME;
>   			break;
>   		}
>
> -		/* Ensure that even if the GPU hangs, we get woken up. */
> -		i915_queue_hangcheck(dev_priv);
> -
> -		timer.function = NULL;
> -		if (timeout || missed_irq(dev_priv, ring)) {
> -			unsigned long expire;
> +		if (intel_breadcrumb_complete(&wait))
> +			break;
>
> -			setup_timer_on_stack(&timer, fake_irq, (unsigned long)current);
> -			expire = missed_irq(dev_priv, ring) ? jiffies + 1 : timeout_expire;
> -			mod_timer(&timer, expire);
> -		}
> +wakeup:		set_task_state(wait.task, state);
>
> -		io_schedule();
> +		/* Ensure our read of the seqno is coherent so that we
> +		 * do not "miss an interrupt" (i.e. if this is the last
> +		 * request and the seqno write from the GPU is not visible
> +		 * by the time the interrupt fires, we will see that the
> +		 * request is incomplete and go back to sleep awaiting
> +		 * another interrupt that will never come.)
> +		 *
> +		 * Strictly, we only need to do this once after an interrupt,
> +		 * but it is easier and safer to do it every time the waiter
> +		 * is woken.
> +		 */
> +		if (i915_gem_request_completed(req, false))
> +			break;
>
> -		if (timer.function) {
> -			del_singleshot_timer_sync(&timer);
> -			destroy_timer_on_stack(&timer);
> -		}
> +		/* We need to check whether any gpu reset happened in between
> +		 * the request being submitted and now. If a reset has occurred,
> +		 * the request is effectively complete (we either are in the
> +		 * process of or have discarded the rendering and completely
> +		 * reset the GPU. The results of the request are lost and we
> +		 * are free to continue on with the original operation.
> +		 */
> +		if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
> +			break;
>   	}
> -	if (!irq_test_in_progress)
> -		ring->irq_put(ring);
> -
> -	finish_wait(&ring->irq_queue, &wait);
> -
>   out:
> +	intel_engine_remove_breadcrumb(req->ring, &wait);
> +	__set_task_state(wait.task, TASK_RUNNING);
>   	now = ktime_get_raw_ns();
>   	trace_i915_gem_request_wait_end(req);
>
> diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
> index 06ca4082735b..f805d117f3d1 100644
> --- a/drivers/gpu/drm/i915/i915_gpu_error.c
> +++ b/drivers/gpu/drm/i915/i915_gpu_error.c
> @@ -900,7 +900,7 @@ static void i915_record_ring_state(struct drm_device *dev,
>   		ering->instdone = I915_READ(GEN2_INSTDONE);
>   	}
>
> -	ering->waiting = waitqueue_active(&ring->irq_queue);
> +	ering->waiting = intel_engine_has_waiter(ring);
>   	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
>   	ering->seqno = ring->get_seqno(ring, false);
>   	ering->acthd = intel_ring_get_active_head(ring);
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 5f88869e2207..d250b4721a6a 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -1000,8 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
>   		return;
>
>   	trace_i915_gem_request_notify(ring);
> -
> -	wake_up_all(&ring->irq_queue);
> +	intel_engine_wakeup(ring);
>   }
>
>   static void vlv_c0_read(struct drm_i915_private *dev_priv,
> @@ -1083,7 +1082,7 @@ static bool any_waiters(struct drm_i915_private *dev_priv)
>   	int i;
>
>   	for_each_ring(ring, dev_priv, i)
> -		if (ring->irq_refcount)
> +		if (intel_engine_has_waiter(ring))
>   			return true;
>
>   	return false;
> @@ -2411,7 +2410,7 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
>
>   	/* Wake up __wait_seqno, potentially holding dev->struct_mutex. */
>   	for_each_ring(ring, dev_priv, i)
> -		wake_up_all(&ring->irq_queue);
> +		intel_engine_wakeup(ring);

This is from process context without a lock or synchronize rcu. I'll 
comment on it at the implementation site as well.

>
>   	/* Wake up intel_crtc_wait_for_pending_flips, holding crtc->mutex. */
>   	wake_up_all(&dev_priv->pending_flip_queue);
> @@ -2986,16 +2985,17 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
>   			if (ring_idle(ring, seqno)) {
>   				ring->hangcheck.action = HANGCHECK_IDLE;
>
> -				if (waitqueue_active(&ring->irq_queue)) {
> +				if (intel_engine_has_waiter(ring)) {
>   					/* Issue a wake-up to catch stuck h/w. */
>   					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
> -						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
> +						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
>   							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
>   								  ring->name);
>   						else
>   							DRM_INFO("Fake missed irq on %s\n",
>   								 ring->name);
> -						wake_up_all(&ring->irq_queue);
> +
> +						intel_engine_enable_fake_irq(ring);
>   					}
>   					/* Safeguard against driver failure */
>   					ring->hangcheck.score += BUSY;
> diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> new file mode 100644
> index 000000000000..a9a199bca2c2
> --- /dev/null
> +++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> @@ -0,0 +1,274 @@
> +/*
> + * Copyright © 2015 Intel Corporation
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice (including the next
> + * paragraph) shall be included in all copies or substantial portions of the
> + * Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> + * IN THE SOFTWARE.
> + *
> + */
> +
> +#include "i915_drv.h"
> +
> +static void intel_breadcrumbs_fake_irq(unsigned long data)
> +{
> +	struct intel_breadcrumbs *b = (struct intel_breadcrumbs *)data;
> +	struct task_struct *task;
> +
> +	/*
> +	 * The timer persists in case we cannot enable interrupts,
> +	 * or if we have previously seen seqno/interrupt incoherency
> +	 * ("missed interrupt" syndrome). Here the worker will wake up
> +	 * every jiffie in order to kick the oldest waiter to do the
> +	 * coherent seqno check.
> +	 */
> +
> +	task = READ_ONCE(b->first_waiter);
> +	if (task) {
> +		wake_up_process(task);

Put a comment here describing why a task cannot exit and become invalid 
between sampling and wakeup?

Or we could afford a spinlock here since this fires really infrequently?

Or even intel_engine_wakeup?

> +		mod_timer(&b->fake_irq, jiffies + 1);
> +	}
> +}
> +
> +static void irq_enable(struct intel_engine_cs *engine)
> +{
> +	WARN_ON(!engine->irq_get(engine));
> +}
> +
> +static void irq_disable(struct intel_engine_cs *engine)
> +{
> +	engine->irq_put(engine);
> +}

These helpers don't do much and only have one call site each?

> +
> +static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
> +{
> +	struct intel_engine_cs *engine =
> +		container_of(b, struct intel_engine_cs, breadcrumbs);
> +	bool noirq;
> +
> +	if (b->rpm_wakelock)
> +		return;
> +
> +	/* Since we are waiting on a request, the GPU should be busy
> +	 * and should have its own rpm reference. For completeness,
> +	 * record an rpm reference for ourselves to cover the
> +	 * interrupt we unmask.
> +	 */
> +	intel_runtime_pm_get_noresume(engine->i915);
> +	b->rpm_wakelock = true;
> +
> +	/* No interrupts? Kick the waiter every jiffie! */
> +	noirq = true;
> +	if (intel_irqs_enabled(engine->i915)) {
> +		noirq = test_bit(engine->id,
> +				 &engine->i915->gpu_error.missed_irq_rings);
> +		if (!test_bit(engine->id,
> +			      &engine->i915->gpu_error.test_irq_rings)) {
> +			irq_enable(engine);
> +			b->irq_enabled = true;
> +		}
> +	}
> +	if (noirq)
> +		mod_timer(&b->fake_irq, jiffies + 1);
> +}
> +
> +static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
> +{
> +	struct intel_engine_cs *engine =
> +		container_of(b, struct intel_engine_cs, breadcrumbs);
> +
> +	if (!b->rpm_wakelock)
> +		return;
> +
> +	if (b->irq_enabled) {
> +		irq_disable(engine);
> +		b->irq_enabled = false;
> +	}
> +
> +	intel_runtime_pm_put(engine->i915);
> +	b->rpm_wakelock = false;
> +}

Maybe put assert_spin_locked in the above two.

> +
> +inline struct intel_breadcrumb *to_crumb(struct rb_node *node)
> +{
> +	return container_of(node, struct intel_breadcrumb, node);
> +}
> +
> +bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
> +				 struct intel_breadcrumb *wait)
> +{
> +	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +	u32 seqno = engine->get_seqno(engine, true);
> +	struct rb_node **p, *parent, *completed;
> +	bool first;
> +
> +	spin_lock(&b->lock);
> +
> +	/* Insert the request into the retirment ordered list
> +	 * of waiters by walking the rbtree. If we are the oldest
> +	 * seqno in the tree (the first to be retired), then
> +	 * set ourselves as the bottom-half.
> +	 *
> +	 * As we descend the tree, prune completed branches since we hold the
> +	 * spinlock we know that the first_waiter must be delayed and can
> +	 * reduce some of the sequential wake up latency if we take action
> +	 * ourselves and wake up the copmleted tasks in parallel.
> +	 */

Why it is interesting to do it both from add and remove breadcrumb 
paths? Wouldn't it be sufficient to do it only on remove?

> +	first = true;
> +	parent = NULL;
> +	completed = NULL;
> +	p = &b->requests.rb_node;
> +	while (*p) {
> +		parent = *p;
> +		if (i915_seqno_passed(wait->seqno, to_crumb(parent)->seqno)) {
> +			p = &parent->rb_right;
> +			if (i915_seqno_passed(seqno, to_crumb(parent)->seqno))
> +				completed = parent;
> +			else
> +				first = false;
> +		} else
> +			p = &parent->rb_left;
> +	}
> +	rb_link_node(&wait->node, parent, p);
> +	rb_insert_color(&wait->node, &b->requests);
> +
> +	if (completed != NULL) {
> +		struct rb_node *next = rb_next(completed);
> +
> +		if (next && next != &wait->node) {
> +			smp_store_mb(b->first_waiter, to_crumb(next)->task);
> +			__intel_breadcrumbs_enable_irq(b);
> +			wake_up_process(to_crumb(next)->task);

I don't get this, why it is waking up the one after completed? Just to 
anticipate it might be completed soon?

> +		}
> +
> +		do {
> +			struct intel_breadcrumb *crumb = to_crumb(completed);
> +			completed = rb_prev(completed);
> +
> +			rb_erase(&crumb->node, &b->requests);
> +			RB_CLEAR_NODE(&crumb->node);
> +			wake_up_process(crumb->task);
> +		} while (completed != NULL);
> +	}
> +
> +	if (first)
> +		smp_store_mb(b->first_waiter, wait->task);
> +	BUG_ON(b->first_waiter == NULL);

I object your honour! :) Let the user ssh in and reboot cleanly even if 
graphics stack is stuck.

> +
> +	spin_unlock(&b->lock);
> +
> +	return first;
> +}
> +
> +void intel_engine_enable_breadcrumb_irq(struct intel_engine_cs *engine)
> +{
> +	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +
> +	spin_lock(&b->lock);
> +	__intel_breadcrumbs_enable_irq(b);
> +	spin_unlock(&b->lock);
> +}
> +
> +void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
> +{
> +	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
> +}
> +
> +void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
> +				    struct intel_breadcrumb *wait)
> +{
> +	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +
> +	/* Quick check to see if this waiter was already decoupled from
> +	 * the tree by the bottom-half to avoid contention on the spinlock
> +	 * by the herd.
> +	 */
> +	if (RB_EMPTY_NODE(&wait->node))
> +		return;
> +
> +	spin_lock(&b->lock);
> +
> +	if (b->first_waiter == wait->task) {
> +		struct rb_node *next;
> +		struct task_struct *task;
> +
> +		/* We are the current bottom-half. Find the next candidate,
> +		 * the first waiter in the queue on the remaining oldest
> +		 * request. As multiple seqnos may complete in the time it
> +		 * takes us to wake up and find the next waiter, we have to
> +		 * wake up that waiter for it to perform its own coherent
> +		 * completion check.
> +		 */
> +		next = rb_next(&wait->node);
> +		if (next) {
> +			/* If the next waiter is already complete,
> +			 * wake it up and continue onto the next waiter. So
> +			 * if have a small herd, they will wake up in parallel
> +			 * rather than sequentially, which should reduce
> +			 * the overall latency in waking all the completed
> +			 * clients.
> +			 */
> +			u32 seqno = engine->get_seqno(engine, true);
> +			while (i915_seqno_passed(seqno,
> +						 to_crumb(next)->seqno)) {
> +				struct rb_node *n = rb_next(next);
> +
> +				rb_erase(next, &b->requests);
> +				RB_CLEAR_NODE(next);
> +				wake_up_process(to_crumb(next)->task);
> +
> +				next = n;
> +				if (next == NULL)
> +					break;
> +			}
> +		}
> +		task = next ? to_crumb(next)->task : NULL;
> +
> +		smp_store_mb(b->first_waiter, task);
> +		if (task) {
> +			/* In our haste, we may have completed the first waiter
> +			 * before we enabled the interrupt. Do so now as we
> +			 * have a second waiter for a future seqno. Afterwards,
> +			 * we have to wake up that waiter in case we missed
> +			 * the interrupt, or if we have to handle an
> +			 * exception rather than a seqno completion.
> +			 */
> +			__intel_breadcrumbs_enable_irq(b);
> +			wake_up_process(task);
> +		} else
> +			__intel_breadcrumbs_disable_irq(b);
> +	}
> +
> +	if (!RB_EMPTY_NODE(&wait->node))
> +		rb_erase(&wait->node, &b->requests);
> +	spin_unlock(&b->lock);
> +}
> +
> +void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
> +{
> +	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +
> +	spin_lock_init(&b->lock);
> +	setup_timer(&b->fake_irq, intel_breadcrumbs_fake_irq, (unsigned long)b);
> +}
> +
> +void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
> +{
> +	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> +
> +	del_timer_sync(&b->fake_irq);
> +}
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index 7030ff526941..780aa6d390aa 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -1898,6 +1898,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
>   	i915_cmd_parser_fini_ring(ring);
>   	i915_gem_batch_pool_fini(&ring->batch_pool);
>
> +	intel_engine_fini_breadcrumbs(ring);
> +
>   	if (ring->status_page.obj) {
>   		kunmap(sg_page(ring->status_page.obj->pages->sgl));
>   		ring->status_page.obj = NULL;
> @@ -1915,10 +1917,11 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
>   	ring->buffer = NULL;
>
>   	ring->dev = dev;
> +	ring->i915 = to_i915(dev);
>   	INIT_LIST_HEAD(&ring->active_list);
>   	INIT_LIST_HEAD(&ring->request_list);
>   	i915_gem_batch_pool_init(dev, &ring->batch_pool);
> -	init_waitqueue_head(&ring->irq_queue);
> +	intel_engine_init_breadcrumbs(ring);
>
>   	INIT_LIST_HEAD(&ring->buffers);
>   	INIT_LIST_HEAD(&ring->execlist_queue);
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
> index 69dd69e46fa9..e90c28e2da31 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.c
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
> @@ -2152,6 +2152,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
>   	WARN_ON(ring->buffer);
>
>   	ring->dev = dev;
> +	ring->i915 = to_i915(dev);
>   	INIT_LIST_HEAD(&ring->active_list);
>   	INIT_LIST_HEAD(&ring->request_list);
>   	INIT_LIST_HEAD(&ring->execlist_queue);
> @@ -2159,7 +2160,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
>   	i915_gem_batch_pool_init(dev, &ring->batch_pool);
>   	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
>
> -	init_waitqueue_head(&ring->irq_queue);
> +	intel_engine_init_breadcrumbs(ring);
>
>   	ringbuf = intel_engine_create_ringbuffer(ring, 32 * PAGE_SIZE);
>   	if (IS_ERR(ringbuf)) {
> @@ -2223,6 +2224,8 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring)
>
>   	i915_cmd_parser_fini_ring(ring);
>   	i915_gem_batch_pool_fini(&ring->batch_pool);
> +	intel_engine_fini_breadcrumbs(ring);
> +
>   	ring->dev = NULL;
>   }
>
> diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
> index 49574ffe54bc..281ed2c92b91 100644
> --- a/drivers/gpu/drm/i915/intel_ringbuffer.h
> +++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
> @@ -157,9 +157,35 @@ struct  intel_engine_cs {
>   #define LAST_USER_RING (VECS + 1)
>   	u32		mmio_base;
>   	struct		drm_device *dev;
> +	struct drm_i915_private *i915;
>   	struct intel_ringbuffer *buffer;
>   	struct list_head buffers;
>
> +	/* Rather than have every client wait upon all user interrupts,
> +	 * with the herd waking after every interrupt and each doing the
> +	 * heavyweight seqno dance, we delegate the task (of being the
> +	 * bottom-half of the user interrupt) to the first client. After
> +	 * every interrupt, we wake up one client, who does the heavyweight
> +	 * coherent seqno read and either goes back to sleep (if incomplete),
> +	 * or wakes up all the completed clients in parallel, before then
> +	 * transferring the bottom-half status to the next client in the queue.
> +	 *
> +	 * Compared to walking the entire list of waiters in a single dedicated
> +	 * bottom-half, we reduce the latency of the first waiter by avoiding
> +	 * a context switch, but incur additional coherent seqno reads when
> +	 * following the chain of request breadcrumbs. Since it is most likely
> +	 * that we have a single client waiting on each seqno, then reducing
> +	 * the overhead of waking that client is much preferred.
> +	 */
> +	struct intel_breadcrumbs {
> +		spinlock_t lock; /* protects the lists of requests */
> +		struct rb_root requests; /* sorted by retirement */
> +		struct task_struct *first_waiter; /* bh for user interrupts */
> +		struct timer_list fake_irq; /* used after a missed interrupt */
> +		bool irq_enabled;
> +		bool rpm_wakelock;
> +	} breadcrumbs;
> +
>   	/*
>   	 * A pool of objects to use as shadow copies of client batch buffers
>   	 * when the command parser is enabled. Prevents the client from
> @@ -303,8 +329,6 @@ struct  intel_engine_cs {
>
>   	bool gpu_caches_dirty;
>
> -	wait_queue_head_t irq_queue;
> -
>   	struct intel_context *default_context;
>   	struct intel_context *last_context;
>
> @@ -510,4 +534,39 @@ void intel_ring_reserved_space_end(struct intel_ringbuffer *ringbuf);
>   /* Legacy ringbuffer specific portion of reservation code: */
>   int intel_ring_reserve_space(struct drm_i915_gem_request *request);
>
> +/* intel_breadcrumbs.c -- user interrupt bottom-half for waiters */
> +struct intel_breadcrumb {
> +	struct rb_node node;
> +	struct task_struct *task;
> +	u32 seqno;
> +};
> +void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine);
> +static inline void intel_breadcrumb_init(struct intel_breadcrumb *wait,
> +					 u32 seqno)
> +{
> +	wait->task = current;
> +	wait->seqno = seqno;
> +}
> +static inline bool intel_breadcrumb_complete(struct intel_breadcrumb *wait)
> +{
> +	return RB_EMPTY_NODE(&wait->node);
> +}
> +bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
> +				 struct intel_breadcrumb *wait);
> +void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
> +				    struct intel_breadcrumb *wait);
> +static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
> +{
> +	return READ_ONCE(engine->breadcrumbs.first_waiter);
> +}
> +static inline void intel_engine_wakeup(struct intel_engine_cs *engine)
> +{
> +	struct task_struct *task = READ_ONCE(engine->breadcrumbs.first_waiter);
> +	if (task)
> +		wake_up_process(task);

And here definitely put a comment saying why this is safe without the 
spinlock.

Actually seeing how it is called from irq context and process context I 
think it will need a lock.

Maybe you can add an irq flavour is lockless variant is really 
beneficial from the user interrupt handler?

> +}
> +void intel_engine_enable_breadcrumb_irq(struct intel_engine_cs *engine);
> +void intel_engine_enable_fake_irq(struct intel_engine_cs *engine);
> +void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
> +
>   #endif /* _INTEL_RINGBUFFER_H_ */
>

Regards,

Tvrtko
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Re: [PATCH 15/32] drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

On Mon, Dec 14, 2015 at 12:21:32PM +0000, Tvrtko Ursulin wrote:
> >@@ -1229,18 +1219,13 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
> >  			s64 *timeout,
> >  			struct intel_rps_client *rps)
> >  {
> >-	struct intel_engine_cs *ring = i915_gem_request_get_ring(req);
> >-	struct drm_device *dev = ring->dev;
> >-	struct drm_i915_private *dev_priv = dev->dev_private;
> >-	const bool irq_test_in_progress =
> >-		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
> >  	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
> >-	DEFINE_WAIT(wait);
> >-	unsigned long timeout_expire;
> >+	struct intel_breadcrumb wait;
> >+	unsigned long timeout_remain;
> >  	s64 before, now;
> >-	int ret;
> >+	int ret = 0;
> >
> >-	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
> >+	might_sleep();
> 
> Why this suddenly?

No reason other than reading other patches and thought this would make
good annotation for this function.

> >  	/* Wake up __wait_seqno, potentially holding dev->struct_mutex. */
> >  	for_each_ring(ring, dev_priv, i)
> >-		wake_up_all(&ring->irq_queue);
> >+		intel_engine_wakeup(ring);
> 
> This is from process context without a lock or synchronize rcu. I'll
> comment on it at the implementation site as well.

True. We could just do rcu_read_lock() here.
 
> >
> >  	/* Wake up intel_crtc_wait_for_pending_flips, holding crtc->mutex. */
> >  	wake_up_all(&dev_priv->pending_flip_queue);
> >@@ -2986,16 +2985,17 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
> >  			if (ring_idle(ring, seqno)) {
> >  				ring->hangcheck.action = HANGCHECK_IDLE;
> >
> >-				if (waitqueue_active(&ring->irq_queue)) {
> >+				if (intel_engine_has_waiter(ring)) {
> >  					/* Issue a wake-up to catch stuck h/w. */
> >  					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
> >-						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
> >+						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
> >  							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
> >  								  ring->name);
> >  						else
> >  							DRM_INFO("Fake missed irq on %s\n",
> >  								 ring->name);
> >-						wake_up_all(&ring->irq_queue);
> >+
> >+						intel_engine_enable_fake_irq(ring);
> >  					}
> >  					/* Safeguard against driver failure */
> >  					ring->hangcheck.score += BUSY;
> >diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> >new file mode 100644
> >index 000000000000..a9a199bca2c2
> >--- /dev/null
> >+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
> >@@ -0,0 +1,274 @@
> >+/*
> >+ * Copyright © 2015 Intel Corporation
> >+ *
> >+ * Permission is hereby granted, free of charge, to any person obtaining a
> >+ * copy of this software and associated documentation files (the "Software"),
> >+ * to deal in the Software without restriction, including without limitation
> >+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> >+ * and/or sell copies of the Software, and to permit persons to whom the
> >+ * Software is furnished to do so, subject to the following conditions:
> >+ *
> >+ * The above copyright notice and this permission notice (including the next
> >+ * paragraph) shall be included in all copies or substantial portions of the
> >+ * Software.
> >+ *
> >+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> >+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> >+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
> >+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
> >+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
> >+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
> >+ * IN THE SOFTWARE.
> >+ *
> >+ */
> >+
> >+#include "i915_drv.h"
> >+
> >+static void intel_breadcrumbs_fake_irq(unsigned long data)
> >+{
> >+	struct intel_breadcrumbs *b = (struct intel_breadcrumbs *)data;
> >+	struct task_struct *task;
> >+
> >+	/*
> >+	 * The timer persists in case we cannot enable interrupts,
> >+	 * or if we have previously seen seqno/interrupt incoherency
> >+	 * ("missed interrupt" syndrome). Here the worker will wake up
> >+	 * every jiffie in order to kick the oldest waiter to do the
> >+	 * coherent seqno check.
> >+	 */
> >+
> >+	task = READ_ONCE(b->first_waiter);
> >+	if (task) {
> >+		wake_up_process(task);
> 
> Put a comment here describing why a task cannot exit and become
> invalid between sampling and wakeup?
> 
> Or we could afford a spinlock here since this fires really infrequently?

This is softirq context, so means we have to bump the weight
of all our locks. I didn't want to do that, so...
 
> Or even intel_engine_wakeup?

Only because I was using intel_breadcrumbs here. I was thinking of
if (intel_engine_wakeup(engine))
	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);

Ok, that looks better. I'll have to check up on softirq context vs rcu,
I think it is safe as the RCU grace period cannot expire, but I will
have to double check.

> >+static void irq_enable(struct intel_engine_cs *engine)
> >+{
> >+	WARN_ON(!engine->irq_get(engine));
> >+}
> >+
> >+static void irq_disable(struct intel_engine_cs *engine)
> >+{
> >+	engine->irq_put(engine);
> >+}
> 
> These helpers don't do much and only have one call site each?

Later patches.

> >+static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
> >+{
> >+	struct intel_engine_cs *engine =
> >+		container_of(b, struct intel_engine_cs, breadcrumbs);
> >+
> >+	if (!b->rpm_wakelock)
> >+		return;
> >+
> >+	if (b->irq_enabled) {
> >+		irq_disable(engine);
> >+		b->irq_enabled = false;
> >+	}
> >+
> >+	intel_runtime_pm_put(engine->i915);
> >+	b->rpm_wakelock = false;
> >+}
> 
> Maybe put assert_spin_locked in the above two.

Ok.
 
> >+inline struct intel_breadcrumb *to_crumb(struct rb_node *node)
> >+{
> >+	return container_of(node, struct intel_breadcrumb, node);
> >+}
> >+
> >+bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
> >+				 struct intel_breadcrumb *wait)
> >+{
> >+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
> >+	u32 seqno = engine->get_seqno(engine, true);
> >+	struct rb_node **p, *parent, *completed;
> >+	bool first;
> >+
> >+	spin_lock(&b->lock);
> >+
> >+	/* Insert the request into the retirment ordered list
> >+	 * of waiters by walking the rbtree. If we are the oldest
> >+	 * seqno in the tree (the first to be retired), then
> >+	 * set ourselves as the bottom-half.
> >+	 *
> >+	 * As we descend the tree, prune completed branches since we hold the
> >+	 * spinlock we know that the first_waiter must be delayed and can
> >+	 * reduce some of the sequential wake up latency if we take action
> >+	 * ourselves and wake up the copmleted tasks in parallel.
> >+	 */
> 
> Why it is interesting to do it both from add and remove breadcrumb
> paths? Wouldn't it be sufficient to do it only on remove?

Observation of heavily contended scenarios show processes getting
between in the interrupt and the bottom-half. So by seeing if we can
prune the tree, we may be able to advance the bottom-half quicker.

> >+		if (next && next != &wait->node) {
> >+			smp_store_mb(b->first_waiter, to_crumb(next)->task);
> >+			__intel_breadcrumbs_enable_irq(b);
> >+			wake_up_process(to_crumb(next)->task);
> 
> I don't get this, why it is waking up the one after completed? Just
> to anticipate it might be completed soon?

No. Because we may miss the interrupt in the process of enabling it.

> >+		}
> >+
> >+		do {
> >+			struct intel_breadcrumb *crumb = to_crumb(completed);
> >+			completed = rb_prev(completed);
> >+
> >+			rb_erase(&crumb->node, &b->requests);
> >+			RB_CLEAR_NODE(&crumb->node);
> >+			wake_up_process(crumb->task);
> >+		} while (completed != NULL);
> >+	}
> >+
> >+	if (first)
> >+		smp_store_mb(b->first_waiter, wait->task);
> >+	BUG_ON(b->first_waiter == NULL);
> 
> I object your honour! :) Let the user ssh in and reboot cleanly even
> if graphics stack is stuck.

You should still be able to ssh and kill the box. I object to using
WARN_ON inappropriately.

> >+static inline void intel_engine_wakeup(struct intel_engine_cs *engine)
> >+{
> >+	struct task_struct *task = READ_ONCE(engine->breadcrumbs.first_waiter);
> >+	if (task)
> >+		wake_up_process(task);
> 
> And here definitely put a comment saying why this is safe without
> the spinlock.
> 
> Actually seeing how it is called from irq context and process
> context I think it will need a lock.

Ok, we can look at improving the commentary.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[PATCH] drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

One particularly stressful scenario consists of many independent tasks
all competing for GPU time and waiting upon the results (e.g. realtime
transcoding of many, many streams). One bottleneck in particular is that
each client waits on its own results, but every client is woken up after
every batchbuffer - hence the thunder of hooves as then every client must
do its heavyweight dance to read a coherent seqno to see if it is the
lucky one.

Ideally, we only want one client to wake up after the interrupt and
check its request for completion. Since the requests must retire in
order, we can select the first client on the oldest request to be woken.
Once that client has completed his wait, we can then wake up the
next client and so on. However, all clients then incur latency as every
process in the chain may be delayed for scheduling - this may also then
cause some priority inversion. To reduce the latency, when a client
is added or removed from the list, we scan the tree for completed
seqno and wake up all the completed waiters in parallel.

v2: Convert from a kworker per engine into a dedicated kthread for the
bottom-half.
v3: Rename request members and tweak comments.
v4: Use a per-engine spinlock in the breadcrumbs bottom-half.
v5: Fix race in locklessly checking waiter status and kicking the task on
adding a new waiter.
v6: Fix deciding when to force the timer to hide missing interrupts.
v7: Move the bottom-half from the kthread to the first client process.
v8: Reword a few comments
v9: Break the busy loop when the interrupt is unmasked or has fired.
v10: Comments, unnecessary churn, better debugging from Tvrtko
v11: Wake all completed waiters on removing the current bottom-half to
reduce the latency of waking up a herd of clients all waiting on the
same request.
v12: Rearrange missed-interrupt fault injection so that it works with
igt/drv_missed_irq_hang
v13: Rename intel_breadcrumb and friends to intel_wait in preparation
for signal handling.
v14: RCU commentary, assert_spin_locked

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
---
 drivers/gpu/drm/i915/Makefile            |   1 +
 drivers/gpu/drm/i915/i915_debugfs.c      |  19 +-
 drivers/gpu/drm/i915/i915_drv.h          |  32 +++-
 drivers/gpu/drm/i915/i915_gem.c          | 140 ++++++---------
 drivers/gpu/drm/i915/i915_gpu_error.c    |   2 +-
 drivers/gpu/drm/i915/i915_irq.c          |  20 +--
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 293 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c         |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c  |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  68 ++++++-
 10 files changed, 477 insertions(+), 108 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/intel_breadcrumbs.c

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 1e9895b9a546..99ce591c8574 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -37,6 +37,7 @@ i915-y += i915_cmd_parser.o \
 	  i915_gem_userptr.o \
 	  i915_gpu_error.o \
 	  i915_trace_points.o \
+	  intel_breadcrumbs.o \
 	  intel_lrc.o \
 	  intel_mocs.o \
 	  intel_ringbuffer.o \
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 2fd2b8214f01..ff76a819b352 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -730,10 +730,22 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
 static void i915_ring_seqno_info(struct seq_file *m,
 				 struct intel_engine_cs *ring)
 {
+	struct rb_node *rb;
+
 	if (ring->get_seqno) {
 		seq_printf(m, "Current sequence (%s): %x\n",
 			   ring->name, ring->get_seqno(ring, false));
 	}
+
+	spin_lock(&ring->breadcrumbs.lock);
+	for (rb = rb_first(&ring->breadcrumbs.waiters);
+	     rb != NULL;
+	     rb = rb_next(rb)) {
+		struct intel_wait *w = container_of(rb, typeof(*w), node);
+		seq_printf(m, "Waiting (%s): %s [%d] on %x\n",
+			   ring->name, w->task->comm, w->task->pid, w->seqno);
+	}
+	spin_unlock(&ring->breadcrumbs.lock);
 }
 
 static int i915_gem_seqno_info(struct seq_file *m, void *data)
@@ -1356,8 +1368,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 
 	for_each_ring(ring, dev_priv, i) {
 		seq_printf(m, "%s:\n", ring->name);
-		seq_printf(m, "\tseqno = %x [current %x]\n",
-			   ring->hangcheck.seqno, seqno[i]);
+		seq_printf(m, "\tseqno = %x [current %x], waiters? %d\n",
+			   ring->hangcheck.seqno, seqno[i],
+			   intel_engine_has_waiter(ring));
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
 			   (long long)acthd[i]);
@@ -2328,7 +2341,7 @@ static int count_irq_waiters(struct drm_i915_private *i915)
 	int i;
 
 	for_each_ring(ring, i915, i)
-		count += ring->irq_refcount;
+		count += intel_engine_has_waiter(ring);
 
 	return count;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 626f7acca074..495f5ca95c5b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1385,7 +1385,7 @@ struct i915_gpu_error {
 #define I915_STOP_RING_ALLOW_WARN      (1 << 30)
 
 	/* For missed irq/seqno simulation. */
-	unsigned int test_irq_rings;
+	unsigned long test_irq_rings;
 };
 
 enum modeset_restore {
@@ -2838,7 +2838,6 @@ ibx_disable_display_interrupt(struct drm_i915_private *dev_priv, uint32_t bits)
 	ibx_display_interrupt_update(dev_priv, bits, 0);
 }
 
-
 /* i915_gem.c */
 int i915_gem_create_ioctl(struct drm_device *dev, void *data,
 			  struct drm_file *file_priv);
@@ -3657,4 +3656,33 @@ static inline void i915_trace_irq_get(struct intel_engine_cs *ring,
 		i915_gem_request_assign(&ring->trace_irq_req, req);
 }
 
+static inline bool __i915_request_irq_complete(struct drm_i915_gem_request *req)
+{
+	/* Ensure our read of the seqno is coherent so that we
+	 * do not "miss an interrupt" (i.e. if this is the last
+	 * request and the seqno write from the GPU is not visible
+	 * by the time the interrupt fires, we will see that the
+	 * request is incomplete and go back to sleep awaiting
+	 * another interrupt that will never come.)
+	 *
+	 * Strictly, we only need to do this once after an interrupt,
+	 * but it is easier and safer to do it every time the waiter
+	 * is woken.
+	 */
+	if (i915_gem_request_completed(req, false))
+		return true;
+
+	/* We need to check whether any gpu reset happened in between
+	 * the request being submitted and now. If a reset has occurred,
+	 * the request is effectively complete (we either are in the
+	 * process of or have discarded the rendering and completely
+	 * reset the GPU. The results of the request are lost and we
+	 * are free to continue on with the original operation.
+	 */
+	if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
+		return true;
+
+	return false;
+}
+
 #endif
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c29714e1406a..7b845eba9cbc 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1121,17 +1121,6 @@ i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
 	return 0;
 }
 
-static void fake_irq(unsigned long data)
-{
-	wake_up_process((struct task_struct *)data);
-}
-
-static bool missed_irq(struct drm_i915_private *dev_priv,
-		       struct intel_engine_cs *ring)
-{
-	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
-}
-
 static unsigned long local_clock_us(unsigned *cpu)
 {
 	unsigned long t;
@@ -1164,7 +1153,9 @@ static bool busywait_stop(unsigned long timeout, unsigned cpu)
 	return this_cpu != cpu;
 }
 
-static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
+static bool __i915_spin_request(struct drm_i915_gem_request *req,
+				struct intel_wait *wait,
+				int state)
 {
 	unsigned long timeout;
 	unsigned cpu;
@@ -1179,31 +1170,30 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 	 * takes to sleep on a request, on the order of a microsecond.
 	 */
 
-	if (req->ring->irq_refcount)
-		return -EBUSY;
-
 	/* Only spin if we know the GPU is processing this request */
 	if (!i915_gem_request_started(req, true))
-		return -EAGAIN;
+		return false;
 
 	timeout = local_clock_us(&cpu) + 5;
-	while (!need_resched()) {
+	do {
 		if (i915_gem_request_completed(req, true))
-			return 0;
+			return true;
 
-		if (signal_pending_state(state, current))
+		if (signal_pending_state(state, wait->task))
 			break;
 
 		if (busywait_stop(timeout, cpu))
 			break;
 
 		cpu_relax_lowlatency();
-	}
 
-	if (i915_gem_request_completed(req, false))
-		return 0;
+		/* Break the loop if we have consumed the timeslice (or been
+		 * preempted) or when either the background thread has
+		 * enabled the interrupt, or the IRQ has fired.
+		 */
+	} while (!need_resched() && wait->task->state == state);
 
-	return -EAGAIN;
+	return false;
 }
 
 /**
@@ -1227,18 +1217,13 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			s64 *timeout,
 			struct intel_rps_client *rps)
 {
-	struct intel_engine_cs *ring = i915_gem_request_get_ring(req);
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	const bool irq_test_in_progress =
-		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
 	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
-	DEFINE_WAIT(wait);
-	unsigned long timeout_expire;
+	struct intel_wait wait;
+	unsigned long timeout_remain;
 	s64 before, now;
-	int ret;
+	int ret = 0;
 
-	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
+	might_sleep();
 
 	if (list_empty(&req->list))
 		return 0;
@@ -1246,7 +1231,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	if (i915_gem_request_completed(req, true))
 		return 0;
 
-	timeout_expire = 0;
+	timeout_remain = MAX_SCHEDULE_TIMEOUT;
 	if (timeout) {
 		if (WARN_ON(*timeout < 0))
 			return -EINVAL;
@@ -1254,83 +1239,66 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 		if (*timeout == 0)
 			return -ETIME;
 
-		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
+		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
 	}
 
-	if (INTEL_INFO(dev_priv)->gen >= 6)
-		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
-
 	/* Record current time in case interrupted by signal, or wedged */
 	trace_i915_gem_request_wait_begin(req);
 	before = ktime_get_raw_ns();
 
-	/* Optimistic spin for the next jiffie before touching IRQs */
-	ret = __i915_spin_request(req, state);
-	if (ret == 0)
-		goto out;
+	if (INTEL_INFO(req->i915)->gen >= 6)
+		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
-	if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) {
-		ret = -ENODEV;
-		goto out;
-	}
+	intel_wait_init(&wait, req->seqno);
+	set_task_state(wait.task, state);
 
-	for (;;) {
-		struct timer_list timer;
+	/* Optimistic spin for the next ~jiffie before touching IRQs */
+	if (intel_engine_add_wait(req->ring, &wait)) {
+		if (__i915_spin_request(req, &wait, state))
+			goto complete;
 
-		prepare_to_wait(&ring->irq_queue, &wait, state);
+		intel_engine_enable_irq(req->ring);
 
-		/* We need to check whether any gpu reset happened in between
-		 * the request being submitted and now. If a reset has occurred,
-		 * the request is effectively complete (we either are in the
-		 * process of or have discarded the rendering and completely
-		 * reset the GPU. The results of the request are lost and we
-		 * are free to continue on with the original operation.
+		/* In order to check that we haven't missed the interrupt
+		 * as we enabled it, we need to kick ourselves to do a
+		 * coherent check on the seqno before we sleep.
 		 */
-		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
-			ret = 0;
-			break;
-		}
-
-		if (i915_gem_request_completed(req, false)) {
-			ret = 0;
-			break;
-		}
+		goto wakeup;
+	}
 
-		if (signal_pending_state(state, current)) {
+	for (;;) {
+		if (signal_pending_state(state, wait.task)) {
 			ret = -ERESTARTSYS;
 			break;
 		}
 
-		if (timeout && time_after_eq(jiffies, timeout_expire)) {
+		/* Ensure that even if the GPU hangs, we get woken up. */
+		i915_queue_hangcheck(req->i915);
+
+		timeout_remain = io_schedule_timeout(timeout_remain);
+		if (timeout_remain == 0) {
 			ret = -ETIME;
 			break;
 		}
 
-		/* Ensure that even if the GPU hangs, we get woken up. */
-		i915_queue_hangcheck(dev_priv);
-
-		timer.function = NULL;
-		if (timeout || missed_irq(dev_priv, ring)) {
-			unsigned long expire;
-
-			setup_timer_on_stack(&timer, fake_irq, (unsigned long)current);
-			expire = missed_irq(dev_priv, ring) ? jiffies + 1 : timeout_expire;
-			mod_timer(&timer, expire);
-		}
+		if (intel_wait_complete(&wait))
+			break;
 
-		io_schedule();
+wakeup:
+		set_task_state(wait.task, state);
 
-		if (timer.function) {
-			del_singleshot_timer_sync(&timer);
-			destroy_timer_on_stack(&timer);
-		}
+		/* Carefully check if the request is complete, giving time
+		 * for the seqno to be visible following the interrupt.
+		 * We also have to check in case we are kicked by the GPU
+		 * reset in order to drop the struct_mutex.
+		 */
+		if (__i915_request_irq_complete(req))
+			break;
 	}
-	if (!irq_test_in_progress)
-		ring->irq_put(ring);
-
-	finish_wait(&ring->irq_queue, &wait);
 
-out:
+complete:
+	intel_engine_remove_wait(req->ring, &wait);
+	__set_task_state(wait.task, TASK_RUNNING);
 	now = ktime_get_raw_ns();
 	trace_i915_gem_request_wait_end(req);
 
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 06ca4082735b..f805d117f3d1 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -900,7 +900,7 @@ static void i915_record_ring_state(struct drm_device *dev,
 		ering->instdone = I915_READ(GEN2_INSTDONE);
 	}
 
-	ering->waiting = waitqueue_active(&ring->irq_queue);
+	ering->waiting = intel_engine_has_waiter(ring);
 	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
 	ering->seqno = ring->get_seqno(ring, false);
 	ering->acthd = intel_ring_get_active_head(ring);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 5ba82a87f3d1..039ab23238a2 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1000,8 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
 		return;
 
 	trace_i915_gem_request_notify(ring);
-
-	wake_up_all(&ring->irq_queue);
+	intel_engine_wakeup(ring);
 }
 
 static void vlv_c0_read(struct drm_i915_private *dev_priv,
@@ -1083,7 +1082,7 @@ static bool any_waiters(struct drm_i915_private *dev_priv)
 	int i;
 
 	for_each_ring(ring, dev_priv, i)
-		if (ring->irq_refcount)
+		if (intel_engine_has_waiter(ring))
 			return true;
 
 	return false;
@@ -2431,9 +2430,6 @@ out:
 static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 			       bool reset_completed)
 {
-	struct intel_engine_cs *ring;
-	int i;
-
 	/*
 	 * Notify all waiters for GPU completion events that reset state has
 	 * been changed, and that they need to restart their wait after
@@ -2441,9 +2437,8 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 	 * a gpu reset pending so that i915_error_work_func can acquire them).
 	 */
 
-	/* Wake up __wait_seqno, potentially holding dev->struct_mutex. */
-	for_each_ring(ring, dev_priv, i)
-		wake_up_all(&ring->irq_queue);
+	/* Wake up i915_wait_request, potentially holding dev->struct_mutex. */
+	intel_kick_waiters(dev_priv);
 
 	/* Wake up intel_crtc_wait_for_pending_flips, holding crtc->mutex. */
 	wake_up_all(&dev_priv->pending_flip_queue);
@@ -3025,16 +3020,17 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 			if (ring_idle(ring, seqno)) {
 				ring->hangcheck.action = HANGCHECK_IDLE;
 
-				if (waitqueue_active(&ring->irq_queue)) {
+				if (intel_engine_has_waiter(ring)) {
 					/* Issue a wake-up to catch stuck h/w. */
 					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
-						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
+						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
 						else
 							DRM_INFO("Fake missed irq on %s\n",
 								 ring->name);
-						wake_up_all(&ring->irq_queue);
+
+						intel_engine_enable_fake_irq(ring);
 					}
 					/* Safeguard against driver failure */
 					ring->hangcheck.score += BUSY;
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
new file mode 100644
index 000000000000..6603451a6b0c
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -0,0 +1,293 @@
+/*
+ * Copyright © 2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+
+static void intel_breadcrumbs_fake_irq(unsigned long data)
+{
+	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
+
+	/*
+	 * The timer persists in case we cannot enable interrupts,
+	 * or if we have previously seen seqno/interrupt incoherency
+	 * ("missed interrupt" syndrome). Here the worker will wake up
+	 * every jiffie in order to kick the oldest waiter to do the
+	 * coherent seqno check.
+	 */
+	rcu_read_lock();
+	if (intel_engine_wakeup(engine))
+		mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+	rcu_read_unlock();
+}
+
+static void irq_enable(struct intel_engine_cs *engine)
+{
+	WARN_ON(!engine->irq_get(engine));
+}
+
+static void irq_disable(struct intel_engine_cs *engine)
+{
+	engine->irq_put(engine);
+}
+
+static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+	bool noirq;
+
+	assert_spin_locked(&b->lock);
+	if (b->rpm_wakelock)
+		return;
+
+	/* Since we are waiting on a request, the GPU should be busy
+	 * and should have its own rpm reference. For completeness,
+	 * record an rpm reference for ourselves to cover the
+	 * interrupt we unmask.
+	 */
+	intel_runtime_pm_get_noresume(engine->i915);
+	b->rpm_wakelock = true;
+
+	/* No interrupts? Kick the waiter every jiffie! */
+	noirq = true;
+	if (intel_irqs_enabled(engine->i915)) {
+		noirq = test_bit(engine->id,
+				 &engine->i915->gpu_error.missed_irq_rings);
+		if (!test_bit(engine->id,
+			      &engine->i915->gpu_error.test_irq_rings)) {
+			irq_enable(engine);
+			b->irq_enabled = true;
+		}
+	}
+	if (noirq)
+		mod_timer(&b->fake_irq, jiffies + 1);
+}
+
+static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+
+	assert_spin_locked(&b->lock);
+	if (!b->rpm_wakelock)
+		return;
+
+	if (b->irq_enabled) {
+		irq_disable(engine);
+		b->irq_enabled = false;
+	}
+
+	intel_runtime_pm_put(engine->i915);
+	b->rpm_wakelock = false;
+}
+
+inline struct intel_wait *to_wait(struct rb_node *node)
+{
+	return container_of(node, struct intel_wait, node);
+}
+
+bool intel_engine_add_wait(struct intel_engine_cs *engine,
+			   struct intel_wait *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	u32 seqno = engine->get_seqno(engine, true);
+	struct rb_node **p, *parent, *completed;
+	bool first;
+
+	spin_lock(&b->lock);
+
+	/* Insert the request into the retirment ordered list
+	 * of waiters by walking the rbtree. If we are the oldest
+	 * seqno in the tree (the first to be retired), then
+	 * set ourselves as the bottom-half.
+	 *
+	 * As we descend the tree, prune completed branches since we hold the
+	 * spinlock we know that the first_waiter must be delayed and can
+	 * reduce some of the sequential wake up latency if we take action
+	 * ourselves and wake up the copmleted tasks in parallel. Also, by
+	 * removing stale elements in the tree, we may be able to reduce the
+	 * ping-pong between the old bottom-half and ourselves as first-waiter.
+	 */
+	first = true;
+	parent = NULL;
+	completed = NULL;
+	p = &b->waiters.rb_node;
+	while (*p) {
+		parent = *p;
+		if (i915_seqno_passed(wait->seqno, to_wait(parent)->seqno)) {
+			p = &parent->rb_right;
+			if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
+				completed = parent;
+			else
+				first = false;
+		} else
+			p = &parent->rb_left;
+	}
+	rb_link_node(&wait->node, parent, p);
+	rb_insert_color(&wait->node, &b->waiters);
+
+	if (completed != NULL) {
+		struct rb_node *next = rb_next(completed);
+
+		if (next && next != &wait->node) {
+			smp_store_mb(b->first_waiter, to_wait(next)->task);
+			__intel_breadcrumbs_enable_irq(b);
+			wake_up_process(to_wait(next)->task);
+		}
+
+		do {
+			struct intel_wait *crumb = to_wait(completed);
+			completed = rb_prev(completed);
+
+			rb_erase(&crumb->node, &b->waiters);
+			RB_CLEAR_NODE(&crumb->node);
+			wake_up_process(crumb->task);
+		} while (completed != NULL);
+	}
+
+	if (first)
+		smp_store_mb(b->first_waiter, wait->task);
+	BUG_ON(b->first_waiter == NULL);
+
+	spin_unlock(&b->lock);
+
+	return first;
+}
+
+void intel_engine_enable_irq(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock(&b->lock);
+	__intel_breadcrumbs_enable_irq(b);
+	spin_unlock(&b->lock);
+}
+
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
+{
+	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+}
+
+void intel_engine_remove_wait(struct intel_engine_cs *engine,
+			      struct intel_wait *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	/* Quick check to see if this waiter was already decoupled from
+	 * the tree by the bottom-half to avoid contention on the spinlock
+	 * by the herd.
+	 */
+	if (RB_EMPTY_NODE(&wait->node))
+		return;
+
+	spin_lock(&b->lock);
+
+	if (b->first_waiter == wait->task) {
+		struct rb_node *next;
+		struct task_struct *task;
+
+		/* We are the current bottom-half. Find the next candidate,
+		 * the first waiter in the queue on the remaining oldest
+		 * request. As multiple seqnos may complete in the time it
+		 * takes us to wake up and find the next waiter, we have to
+		 * wake up that waiter for it to perform its own coherent
+		 * completion check.
+		 */
+		next = rb_next(&wait->node);
+		if (next) {
+			/* If the next waiter is already complete,
+			 * wake it up and continue onto the next waiter. So
+			 * if have a small herd, they will wake up in parallel
+			 * rather than sequentially, which should reduce
+			 * the overall latency in waking all the completed
+			 * clients.
+			 */
+			u32 seqno = engine->get_seqno(engine, true);
+			while (i915_seqno_passed(seqno,
+						 to_wait(next)->seqno)) {
+				struct rb_node *n = rb_next(next);
+
+				rb_erase(next, &b->waiters);
+				RB_CLEAR_NODE(next);
+				wake_up_process(to_wait(next)->task);
+
+				next = n;
+				if (next == NULL)
+					break;
+			}
+		}
+		task = next ? to_wait(next)->task : NULL;
+
+		smp_store_mb(b->first_waiter, task);
+		if (task) {
+			/* In our haste, we may have completed the first waiter
+			 * before we enabled the interrupt. Do so now as we
+			 * have a second waiter for a future seqno. Afterwards,
+			 * we have to wake up that waiter in case we missed
+			 * the interrupt, or if we have to handle an
+			 * exception rather than a seqno completion.
+			 */
+			__intel_breadcrumbs_enable_irq(b);
+			wake_up_process(task);
+		} else
+			__intel_breadcrumbs_disable_irq(b);
+	}
+
+	if (!RB_EMPTY_NODE(&wait->node))
+		rb_erase(&wait->node, &b->waiters);
+	spin_unlock(&b->lock);
+}
+
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock_init(&b->lock);
+	setup_timer(&b->fake_irq,
+		    intel_breadcrumbs_fake_irq,
+		    (unsigned long)engine);
+}
+
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	del_timer_sync(&b->fake_irq);
+}
+
+void intel_kick_waiters(struct drm_i915_private *i915)
+{
+	struct intel_engine_cs *engine;
+	int i;
+
+	/* To avoid the task_struct disappearing beneath us as we wake up
+	 * the process, we must first inspect the task_struct->state under the
+	 * RCU lock, i.e. as we call wake_up_process() we must be holding the
+	 * rcu_read_lock().
+	 */
+	rcu_read_lock();
+	for_each_ring(engine, i915, i)
+		intel_engine_wakeup(engine);
+	rcu_read_unlock();
+}
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 44d792d76e6f..0f8780f94b8c 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1898,6 +1898,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
 
+	intel_engine_fini_breadcrumbs(ring);
+
 	if (ring->status_page.obj) {
 		kunmap(sg_page(ring->status_page.obj->pages->sgl));
 		ring->status_page.obj = NULL;
@@ -1915,10 +1917,11 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
 	ring->buffer = NULL;
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	INIT_LIST_HEAD(&ring->buffers);
 	INIT_LIST_HEAD(&ring->execlist_queue);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 69dd69e46fa9..e90c28e2da31 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2152,6 +2152,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	WARN_ON(ring->buffer);
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	INIT_LIST_HEAD(&ring->execlist_queue);
@@ -2159,7 +2160,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
 	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
 
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	ringbuf = intel_engine_create_ringbuffer(ring, 32 * PAGE_SIZE);
 	if (IS_ERR(ringbuf)) {
@@ -2223,6 +2224,8 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring)
 
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
+	intel_engine_fini_breadcrumbs(ring);
+
 	ring->dev = NULL;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 49574ffe54bc..13b6ffbc540a 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -157,9 +157,35 @@ struct  intel_engine_cs {
 #define LAST_USER_RING (VECS + 1)
 	u32		mmio_base;
 	struct		drm_device *dev;
+	struct drm_i915_private *i915;
 	struct intel_ringbuffer *buffer;
 	struct list_head buffers;
 
+	/* Rather than have every client wait upon all user interrupts,
+	 * with the herd waking after every interrupt and each doing the
+	 * heavyweight seqno dance, we delegate the task (of being the
+	 * bottom-half of the user interrupt) to the first client. After
+	 * every interrupt, we wake up one client, who does the heavyweight
+	 * coherent seqno read and either goes back to sleep (if incomplete),
+	 * or wakes up all the completed clients in parallel, before then
+	 * transferring the bottom-half status to the next client in the queue.
+	 *
+	 * Compared to walking the entire list of waiters in a single dedicated
+	 * bottom-half, we reduce the latency of the first waiter by avoiding
+	 * a context switch, but incur additional coherent seqno reads when
+	 * following the chain of request breadcrumbs. Since it is most likely
+	 * that we have a single client waiting on each seqno, then reducing
+	 * the overhead of waking that client is much preferred.
+	 */
+	struct intel_breadcrumbs {
+		spinlock_t lock; /* protects the lists of requests */
+		struct rb_root waiters; /* sorted by retirement */
+		struct task_struct *first_waiter; /* bh for user interrupts */
+		struct timer_list fake_irq; /* used after a missed interrupt */
+		bool irq_enabled;
+		bool rpm_wakelock;
+	} breadcrumbs;
+
 	/*
 	 * A pool of objects to use as shadow copies of client batch buffers
 	 * when the command parser is enabled. Prevents the client from
@@ -303,8 +329,6 @@ struct  intel_engine_cs {
 
 	bool gpu_caches_dirty;
 
-	wait_queue_head_t irq_queue;
-
 	struct intel_context *default_context;
 	struct intel_context *last_context;
 
@@ -510,4 +534,44 @@ void intel_ring_reserved_space_end(struct intel_ringbuffer *ringbuf);
 /* Legacy ringbuffer specific portion of reservation code: */
 int intel_ring_reserve_space(struct drm_i915_gem_request *request);
 
+/* intel_breadcrumbs.c -- user interrupt bottom-half for waiters */
+struct intel_wait {
+	struct rb_node node;
+	struct task_struct *task;
+	u32 seqno;
+};
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine);
+static inline void intel_wait_init(struct intel_wait *wait, u32 seqno)
+{
+	wait->task = current;
+	wait->seqno = seqno;
+}
+static inline bool intel_wait_complete(struct intel_wait *wait)
+{
+	return RB_EMPTY_NODE(&wait->node);
+}
+bool intel_engine_add_wait(struct intel_engine_cs *engine,
+			   struct intel_wait *wait);
+void intel_engine_remove_wait(struct intel_engine_cs *engine,
+			      struct intel_wait *wait);
+static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
+{
+	return READ_ONCE(engine->breadcrumbs.first_waiter);
+}
+static inline bool intel_engine_wakeup(struct intel_engine_cs *engine)
+{
+	struct task_struct *task = READ_ONCE(engine->breadcrumbs.first_waiter);
+	/* Note that for this not to dangerously chase a dangling pointer,
+	 * the caller is responsible for ensure that the task remain valid for
+	 * wake_up_process() i.e. that the RCU grace period cannot expire.
+	 */
+	if (task)
+		wake_up_process(task);
+	return task != NULL;
+}
+void intel_engine_enable_irq(struct intel_engine_cs *engine);
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine);
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
+void intel_kick_waiters(struct drm_i915_private *i915);
+
 #endif /* _INTEL_RINGBUFFER_H_ */
-- 
2.6.4

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH v16] drm/i915: Slaughter the thundering i915_wait_request herd

[Chris Wilson]

One particularly stressful scenario consists of many independent tasks
all competing for GPU time and waiting upon the results (e.g. realtime
transcoding of many, many streams). One bottleneck in particular is that
each client waits on its own results, but every client is woken up after
every batchbuffer - hence the thunder of hooves as then every client must
do its heavyweight dance to read a coherent seqno to see if it is the
lucky one.

Ideally, we only want one client to wake up after the interrupt and
check its request for completion. Since the requests must retire in
order, we can select the first client on the oldest request to be woken.
Once that client has completed his wait, we can then wake up the
next client and so on. However, all clients then incur latency as every
process in the chain may be delayed for scheduling - this may also then
cause some priority inversion. To reduce the latency, when a client
is added or removed from the list, we scan the tree for completed
seqno and wake up all the completed waiters in parallel.

Using igt/benchmarks/gem_latency, we can demonstrate this effect. The
benchmark measures the number of GPU cycles between completion of a
batch and the client waking up from a call to wait-ioctl. With many
concurrent waiters, with each on a different request, we observe that
the wakeup latency before the patch scales nearly linearly with the
number of waiters (before external factors kick in making the scaling much
worse). After applying the patch, we can see that only the single waiter
for the request is being woken up, providing a constant wakeup latency
for every operation. However, the situation is not quite as rosy for
many waiters on the same request, though to the best of my knowledge this
is much less likely in practice. Here, we can observe that the
concurrent waiters incur extra latency from being woken up by the
solitary bottom-half, rather than directly by the interrupt. This
appears to be scheduler induced (having discounted adverse effects from
having a rbtree walk/erase in the wakeup path), each additional
wake_up_process() costs aproximately 1us on big core. Another effect of
performing the secondary wakeups from the first bottom-half is the
incurred delay this imposes on high priority threads - rather than
immediately returning to userspace and leaving the interrupt handler to
wake the others.

To offset the delay incurred with additional waiters on a request, we
could use a hybrid scheme that did a quick read in the interrupt handler
and dequeued all the completed waiters (incurring the overhead in the
interrupt handler, not the best plan either as we then incur GPU
submission latency) but we would still have to wake up the bottom-half
everytime to do the heavyweight slow read. Or we could only kick the
waiters on the seqno with the same priority as the current task (i.e. in
the realtime waiter scenario, only it is woken up immediately by the
interrupt and simply queues the next waiter before returning to userspace,
minimising its delay at the expense of the chain, and also reducing
contention on its scheduler runqueue). This is effective at avoid long
pauses in the interrupt handler and at avoiding the extra latency in
realtime/high-priority waiters.

v2: Convert from a kworker per engine into a dedicated kthread for the
bottom-half.
v3: Rename request members and tweak comments.
v4: Use a per-engine spinlock in the breadcrumbs bottom-half.
v5: Fix race in locklessly checking waiter status and kicking the task on
adding a new waiter.
v6: Fix deciding when to force the timer to hide missing interrupts.
v7: Move the bottom-half from the kthread to the first client process.
v8: Reword a few comments
v9: Break the busy loop when the interrupt is unmasked or has fired.
v10: Comments, unnecessary churn, better debugging from Tvrtko
v11: Wake all completed waiters on removing the current bottom-half to
reduce the latency of waking up a herd of clients all waiting on the
same request.
v12: Rearrange missed-interrupt fault injection so that it works with
igt/drv_missed_irq_hang
v13: Rename intel_breadcrumb and friends to intel_wait in preparation
for signal handling.
v14: RCU commentary, assert_spin_locked
v15: Hide BUG_ON behind the compiler; report on gem_latency findings.
v16: Sort seqno-groups by priority so that first-waiter has the highest
task priority (and so avoid priority inversion).

Testcase: igt/gem_concurrent_blit
Testcase: igt/benchmarks/gem_latency
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Rogozhkin, Dmitry V" <dmitry.v.rogozhkin@intel.com>
Cc: "Gong, Zhipeng" <zhipeng.gong@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Dave Gordon <david.s.gordon@intel.com>
---
 drivers/gpu/drm/i915/Makefile            |   1 +
 drivers/gpu/drm/i915/i915_debugfs.c      |  19 +-
 drivers/gpu/drm/i915/i915_drv.h          |  32 ++-
 drivers/gpu/drm/i915/i915_gem.c          | 141 +++++--------
 drivers/gpu/drm/i915/i915_gpu_error.c    |   2 +-
 drivers/gpu/drm/i915/i915_irq.c          |  20 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 336 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_lrc.c         |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c  |   5 +-
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  69 ++++++-
 10 files changed, 521 insertions(+), 109 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/intel_breadcrumbs.c

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 1e9895b9a546..99ce591c8574 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -37,6 +37,7 @@ i915-y += i915_cmd_parser.o \
 	  i915_gem_userptr.o \
 	  i915_gpu_error.o \
 	  i915_trace_points.o \
+	  intel_breadcrumbs.o \
 	  intel_lrc.o \
 	  intel_mocs.o \
 	  intel_ringbuffer.o \
diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 2fd2b8214f01..ff76a819b352 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -730,10 +730,22 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
 static void i915_ring_seqno_info(struct seq_file *m,
 				 struct intel_engine_cs *ring)
 {
+	struct rb_node *rb;
+
 	if (ring->get_seqno) {
 		seq_printf(m, "Current sequence (%s): %x\n",
 			   ring->name, ring->get_seqno(ring, false));
 	}
+
+	spin_lock(&ring->breadcrumbs.lock);
+	for (rb = rb_first(&ring->breadcrumbs.waiters);
+	     rb != NULL;
+	     rb = rb_next(rb)) {
+		struct intel_wait *w = container_of(rb, typeof(*w), node);
+		seq_printf(m, "Waiting (%s): %s [%d] on %x\n",
+			   ring->name, w->task->comm, w->task->pid, w->seqno);
+	}
+	spin_unlock(&ring->breadcrumbs.lock);
 }
 
 static int i915_gem_seqno_info(struct seq_file *m, void *data)
@@ -1356,8 +1368,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 
 	for_each_ring(ring, dev_priv, i) {
 		seq_printf(m, "%s:\n", ring->name);
-		seq_printf(m, "\tseqno = %x [current %x]\n",
-			   ring->hangcheck.seqno, seqno[i]);
+		seq_printf(m, "\tseqno = %x [current %x], waiters? %d\n",
+			   ring->hangcheck.seqno, seqno[i],
+			   intel_engine_has_waiter(ring));
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
 			   (long long)acthd[i]);
@@ -2328,7 +2341,7 @@ static int count_irq_waiters(struct drm_i915_private *i915)
 	int i;
 
 	for_each_ring(ring, i915, i)
-		count += ring->irq_refcount;
+		count += intel_engine_has_waiter(ring);
 
 	return count;
 }
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index fa410b23350a..8836c5c00bcb 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1385,7 +1385,7 @@ struct i915_gpu_error {
 #define I915_STOP_RING_ALLOW_WARN      (1 << 30)
 
 	/* For missed irq/seqno simulation. */
-	unsigned int test_irq_rings;
+	unsigned long test_irq_rings;
 };
 
 enum modeset_restore {
@@ -2843,7 +2843,6 @@ ibx_disable_display_interrupt(struct drm_i915_private *dev_priv, uint32_t bits)
 	ibx_display_interrupt_update(dev_priv, bits, 0);
 }
 
-
 /* i915_gem.c */
 int i915_gem_create_ioctl(struct drm_device *dev, void *data,
 			  struct drm_file *file_priv);
@@ -3662,4 +3661,33 @@ static inline void i915_trace_irq_get(struct intel_engine_cs *ring,
 		i915_gem_request_assign(&ring->trace_irq_req, req);
 }
 
+static inline bool __i915_request_irq_complete(struct drm_i915_gem_request *req)
+{
+	/* Ensure our read of the seqno is coherent so that we
+	 * do not "miss an interrupt" (i.e. if this is the last
+	 * request and the seqno write from the GPU is not visible
+	 * by the time the interrupt fires, we will see that the
+	 * request is incomplete and go back to sleep awaiting
+	 * another interrupt that will never come.)
+	 *
+	 * Strictly, we only need to do this once after an interrupt,
+	 * but it is easier and safer to do it every time the waiter
+	 * is woken.
+	 */
+	if (i915_gem_request_completed(req, false))
+		return true;
+
+	/* We need to check whether any gpu reset happened in between
+	 * the request being submitted and now. If a reset has occurred,
+	 * the request is effectively complete (we either are in the
+	 * process of or have discarded the rendering and completely
+	 * reset the GPU. The results of the request are lost and we
+	 * are free to continue on with the original operation.
+	 */
+	if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
+		return true;
+
+	return false;
+}
+
 #endif
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index c29714e1406a..767b36c2b26b 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1121,17 +1121,6 @@ i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
 	return 0;
 }
 
-static void fake_irq(unsigned long data)
-{
-	wake_up_process((struct task_struct *)data);
-}
-
-static bool missed_irq(struct drm_i915_private *dev_priv,
-		       struct intel_engine_cs *ring)
-{
-	return test_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
-}
-
 static unsigned long local_clock_us(unsigned *cpu)
 {
 	unsigned long t;
@@ -1164,7 +1153,9 @@ static bool busywait_stop(unsigned long timeout, unsigned cpu)
 	return this_cpu != cpu;
 }
 
-static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
+static bool __i915_spin_request(struct drm_i915_gem_request *req,
+				struct intel_wait *wait,
+				int state)
 {
 	unsigned long timeout;
 	unsigned cpu;
@@ -1179,31 +1170,30 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
 	 * takes to sleep on a request, on the order of a microsecond.
 	 */
 
-	if (req->ring->irq_refcount)
-		return -EBUSY;
-
 	/* Only spin if we know the GPU is processing this request */
 	if (!i915_gem_request_started(req, true))
-		return -EAGAIN;
+		return false;
 
 	timeout = local_clock_us(&cpu) + 5;
-	while (!need_resched()) {
+	do {
 		if (i915_gem_request_completed(req, true))
-			return 0;
+			return true;
 
-		if (signal_pending_state(state, current))
+		if (signal_pending_state(state, wait->task))
 			break;
 
 		if (busywait_stop(timeout, cpu))
 			break;
 
 		cpu_relax_lowlatency();
-	}
 
-	if (i915_gem_request_completed(req, false))
-		return 0;
+		/* Break the loop if we have consumed the timeslice (or been
+		 * preempted) or when either the background thread has
+		 * enabled the interrupt, or the IRQ itself has fired.
+		 */
+	} while (!need_resched() && wait->task->state == state);
 
-	return -EAGAIN;
+	return false;
 }
 
 /**
@@ -1227,18 +1217,13 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 			s64 *timeout,
 			struct intel_rps_client *rps)
 {
-	struct intel_engine_cs *ring = i915_gem_request_get_ring(req);
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	const bool irq_test_in_progress =
-		ACCESS_ONCE(dev_priv->gpu_error.test_irq_rings) & intel_ring_flag(ring);
 	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
-	DEFINE_WAIT(wait);
-	unsigned long timeout_expire;
+	struct intel_wait wait;
+	unsigned long timeout_remain;
 	s64 before, now;
-	int ret;
+	int ret = 0;
 
-	WARN(!intel_irqs_enabled(dev_priv), "IRQs disabled");
+	might_sleep();
 
 	if (list_empty(&req->list))
 		return 0;
@@ -1246,7 +1231,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	if (i915_gem_request_completed(req, true))
 		return 0;
 
-	timeout_expire = 0;
+	timeout_remain = MAX_SCHEDULE_TIMEOUT;
 	if (timeout) {
 		if (WARN_ON(*timeout < 0))
 			return -EINVAL;
@@ -1254,83 +1239,65 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 		if (*timeout == 0)
 			return -ETIME;
 
-		timeout_expire = jiffies + nsecs_to_jiffies_timeout(*timeout);
+		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
 	}
 
-	if (INTEL_INFO(dev_priv)->gen >= 6)
-		gen6_rps_boost(dev_priv, rps, req->emitted_jiffies);
-
 	/* Record current time in case interrupted by signal, or wedged */
 	trace_i915_gem_request_wait_begin(req);
 	before = ktime_get_raw_ns();
 
-	/* Optimistic spin for the next jiffie before touching IRQs */
-	ret = __i915_spin_request(req, state);
-	if (ret == 0)
-		goto out;
+	if (INTEL_INFO(req->i915)->gen >= 6)
+		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
-	if (!irq_test_in_progress && WARN_ON(!ring->irq_get(ring))) {
-		ret = -ENODEV;
-		goto out;
-	}
-
-	for (;;) {
-		struct timer_list timer;
+	intel_wait_init(&wait, req->seqno);
+	set_task_state(wait.task, state);
 
-		prepare_to_wait(&ring->irq_queue, &wait, state);
+	/* Optimistic spin for the next ~jiffie before touching IRQs */
+	if (intel_engine_add_wait(req->ring, &wait)) {
+		if (__i915_spin_request(req, &wait, state))
+			goto complete;
 
-		/* We need to check whether any gpu reset happened in between
-		 * the request being submitted and now. If a reset has occurred,
-		 * the request is effectively complete (we either are in the
-		 * process of or have discarded the rendering and completely
-		 * reset the GPU. The results of the request are lost and we
-		 * are free to continue on with the original operation.
+		/* In order to check that we haven't missed the interrupt
+		 * as we enabled it, we need to kick ourselves to do a
+		 * coherent check on the seqno before we sleep.
 		 */
-		if (req->reset_counter != i915_reset_counter(&dev_priv->gpu_error)) {
-			ret = 0;
-			break;
-		}
-
-		if (i915_gem_request_completed(req, false)) {
-			ret = 0;
-			break;
-		}
+		if (intel_engine_enable_wait_irq(req->ring, &wait))
+			goto wakeup;
+	}
 
-		if (signal_pending_state(state, current)) {
+	for (;;) {
+		if (signal_pending_state(state, wait.task)) {
 			ret = -ERESTARTSYS;
 			break;
 		}
 
-		if (timeout && time_after_eq(jiffies, timeout_expire)) {
+		/* Ensure that even if the GPU hangs, we get woken up. */
+		i915_queue_hangcheck(req->i915);
+
+		timeout_remain = io_schedule_timeout(timeout_remain);
+		if (timeout_remain == 0) {
 			ret = -ETIME;
 			break;
 		}
 
-		/* Ensure that even if the GPU hangs, we get woken up. */
-		i915_queue_hangcheck(dev_priv);
-
-		timer.function = NULL;
-		if (timeout || missed_irq(dev_priv, ring)) {
-			unsigned long expire;
-
-			setup_timer_on_stack(&timer, fake_irq, (unsigned long)current);
-			expire = missed_irq(dev_priv, ring) ? jiffies + 1 : timeout_expire;
-			mod_timer(&timer, expire);
-		}
+		if (intel_wait_complete(&wait))
+			break;
 
-		io_schedule();
+wakeup:
+		set_task_state(wait.task, state);
 
-		if (timer.function) {
-			del_singleshot_timer_sync(&timer);
-			destroy_timer_on_stack(&timer);
-		}
+		/* Carefully check if the request is complete, giving time
+		 * for the seqno to be visible following the interrupt.
+		 * We also have to check in case we are kicked by the GPU
+		 * reset in order to drop the struct_mutex.
+		 */
+		if (__i915_request_irq_complete(req))
+			break;
 	}
-	if (!irq_test_in_progress)
-		ring->irq_put(ring);
-
-	finish_wait(&ring->irq_queue, &wait);
 
-out:
+complete:
+	intel_engine_remove_wait(req->ring, &wait);
+	__set_task_state(wait.task, TASK_RUNNING);
 	now = ktime_get_raw_ns();
 	trace_i915_gem_request_wait_end(req);
 
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 06ca4082735b..f805d117f3d1 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -900,7 +900,7 @@ static void i915_record_ring_state(struct drm_device *dev,
 		ering->instdone = I915_READ(GEN2_INSTDONE);
 	}
 
-	ering->waiting = waitqueue_active(&ring->irq_queue);
+	ering->waiting = intel_engine_has_waiter(ring);
 	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
 	ering->seqno = ring->get_seqno(ring, false);
 	ering->acthd = intel_ring_get_active_head(ring);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 5ba82a87f3d1..039ab23238a2 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1000,8 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
 		return;
 
 	trace_i915_gem_request_notify(ring);
-
-	wake_up_all(&ring->irq_queue);
+	intel_engine_wakeup(ring);
 }
 
 static void vlv_c0_read(struct drm_i915_private *dev_priv,
@@ -1083,7 +1082,7 @@ static bool any_waiters(struct drm_i915_private *dev_priv)
 	int i;
 
 	for_each_ring(ring, dev_priv, i)
-		if (ring->irq_refcount)
+		if (intel_engine_has_waiter(ring))
 			return true;
 
 	return false;
@@ -2431,9 +2430,6 @@ out:
 static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 			       bool reset_completed)
 {
-	struct intel_engine_cs *ring;
-	int i;
-
 	/*
 	 * Notify all waiters for GPU completion events that reset state has
 	 * been changed, and that they need to restart their wait after
@@ -2441,9 +2437,8 @@ static void i915_error_wake_up(struct drm_i915_private *dev_priv,
 	 * a gpu reset pending so that i915_error_work_func can acquire them).
 	 */
 
-	/* Wake up __wait_seqno, potentially holding dev->struct_mutex. */
-	for_each_ring(ring, dev_priv, i)
-		wake_up_all(&ring->irq_queue);
+	/* Wake up i915_wait_request, potentially holding dev->struct_mutex. */
+	intel_kick_waiters(dev_priv);
 
 	/* Wake up intel_crtc_wait_for_pending_flips, holding crtc->mutex. */
 	wake_up_all(&dev_priv->pending_flip_queue);
@@ -3025,16 +3020,17 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 			if (ring_idle(ring, seqno)) {
 				ring->hangcheck.action = HANGCHECK_IDLE;
 
-				if (waitqueue_active(&ring->irq_queue)) {
+				if (intel_engine_has_waiter(ring)) {
 					/* Issue a wake-up to catch stuck h/w. */
 					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
-						if (!(dev_priv->gpu_error.test_irq_rings & intel_ring_flag(ring)))
+						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
 						else
 							DRM_INFO("Fake missed irq on %s\n",
 								 ring->name);
-						wake_up_all(&ring->irq_queue);
+
+						intel_engine_enable_fake_irq(ring);
 					}
 					/* Safeguard against driver failure */
 					ring->hangcheck.score += BUSY;
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
new file mode 100644
index 000000000000..9f756583a44e
--- /dev/null
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -0,0 +1,336 @@
+/*
+ * Copyright © 2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+
+static void intel_breadcrumbs_fake_irq(unsigned long data)
+{
+	struct intel_engine_cs *engine = (struct intel_engine_cs *)data;
+
+	/*
+	 * The timer persists in case we cannot enable interrupts,
+	 * or if we have previously seen seqno/interrupt incoherency
+	 * ("missed interrupt" syndrome). Here the worker will wake up
+	 * every jiffie in order to kick the oldest waiter to do the
+	 * coherent seqno check.
+	 */
+	rcu_read_lock();
+	if (intel_engine_wakeup(engine))
+		mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+	rcu_read_unlock();
+}
+
+static void irq_enable(struct intel_engine_cs *engine)
+{
+	WARN_ON(!engine->irq_get(engine));
+}
+
+static void irq_disable(struct intel_engine_cs *engine)
+{
+	engine->irq_put(engine);
+}
+
+static bool __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+	bool noirq;
+
+	assert_spin_locked(&b->lock);
+	if (b->rpm_wakelock)
+		return false;
+
+	/* Since we are waiting on a request, the GPU should be busy
+	 * and should have its own rpm reference. For completeness,
+	 * record an rpm reference for ourselves to cover the
+	 * interrupt we unmask.
+	 */
+	intel_runtime_pm_get_noresume(engine->i915);
+	b->rpm_wakelock = true;
+
+	/* No interrupts? Kick the waiter every jiffie! */
+	noirq = true;
+	if (intel_irqs_enabled(engine->i915)) {
+		noirq = test_bit(engine->id,
+				 &engine->i915->gpu_error.missed_irq_rings);
+		if (!test_bit(engine->id,
+			      &engine->i915->gpu_error.test_irq_rings)) {
+			irq_enable(engine);
+			b->irq_enabled = true;
+		}
+	}
+	if (noirq)
+		mod_timer(&b->fake_irq, jiffies + 1);
+
+	return b->irq_enabled;
+}
+
+static void __intel_breadcrumbs_disable_irq(struct intel_breadcrumbs *b)
+{
+	struct intel_engine_cs *engine =
+		container_of(b, struct intel_engine_cs, breadcrumbs);
+
+	assert_spin_locked(&b->lock);
+	if (!b->rpm_wakelock)
+		return;
+
+	if (b->irq_enabled) {
+		irq_disable(engine);
+		b->irq_enabled = false;
+	}
+
+	intel_runtime_pm_put(engine->i915);
+	b->rpm_wakelock = false;
+}
+
+static inline struct intel_wait *to_wait(struct rb_node *node)
+{
+	return container_of(node, struct intel_wait, node);
+}
+
+static inline void __intel_breadcrumbs_finish(struct intel_breadcrumbs *b,
+					      struct intel_wait *wait)
+{
+	assert_spin_locked(&b->lock);
+
+	/* This request is completed, so remove it from the tree, mark it as
+	 * complete, and *then* wake up the associated task.
+	 */
+	rb_erase(&wait->node, &b->waiters);
+	RB_CLEAR_NODE(&wait->node);
+
+	wake_up_process(wait->task); /* implicit smp_wmb() */
+}
+
+bool intel_engine_add_wait(struct intel_engine_cs *engine,
+			   struct intel_wait *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	u32 seqno = engine->get_seqno(engine, true);
+	struct rb_node **p, *parent, *completed;
+	bool first;
+
+	spin_lock(&b->lock);
+
+	/* Insert the request into the retirment ordered list
+	 * of waiters by walking the rbtree. If we are the oldest
+	 * seqno in the tree (the first to be retired), then
+	 * set ourselves as the bottom-half.
+	 *
+	 * As we descend the tree, prune completed branches since we hold the
+	 * spinlock we know that the first_waiter must be delayed and can
+	 * reduce some of the sequential wake up latency if we take action
+	 * ourselves and wake up the copmleted tasks in parallel. Also, by
+	 * removing stale elements in the tree, we may be able to reduce the
+	 * ping-pong between the old bottom-half and ourselves as first-waiter.
+	 */
+	first = true;
+	parent = NULL;
+	completed = NULL;
+	p = &b->waiters.rb_node;
+	while (*p) {
+		parent = *p;
+		if (wait->seqno == to_wait(parent)->seqno) {
+			/* We have multiple waiters on the same seqno, select
+			 * the highest priority task (that with the smallest
+			 * task->prio) to serve as the bottom-half for this
+			 * group.
+			 */
+			if (wait->task->prio > to_wait(parent)->task->prio) {
+				p = &parent->rb_right;
+				first = false;
+			} else
+				p = &parent->rb_left;
+		} else if (i915_seqno_passed(wait->seqno,
+					     to_wait(parent)->seqno)) {
+			p = &parent->rb_right;
+			if (i915_seqno_passed(seqno, to_wait(parent)->seqno))
+				completed = parent;
+			else
+				first = false;
+		} else
+			p = &parent->rb_left;
+	}
+	rb_link_node(&wait->node, parent, p);
+	rb_insert_color(&wait->node, &b->waiters);
+
+	if (completed != NULL) {
+		struct rb_node *next = rb_next(completed);
+
+		if (next && next != &wait->node) {
+			GEM_BUG_ON(first);
+			smp_store_mb(b->first_waiter, to_wait(next)->task);
+			/* If we enable the IRQ, we may have missed the
+			 * interrupt for that seqno, so we have to wake up
+			 * that bottom-half in order to do a coherent check
+			 * in case the seqno passed.
+			 */
+			if (__intel_breadcrumbs_enable_irq(b))
+				wake_up_process(to_wait(next)->task);
+		}
+
+		do {
+			struct intel_wait *crumb = to_wait(completed);
+			completed = rb_prev(completed);
+			__intel_breadcrumbs_finish(b, crumb);
+		} while (completed != NULL);
+	}
+
+	if (first)
+		smp_store_mb(b->first_waiter, wait->task);
+	GEM_BUG_ON(b->first_waiter == NULL);
+
+	spin_unlock(&b->lock);
+
+	return first;
+}
+
+bool intel_engine_enable_wait_irq(struct intel_engine_cs *engine,
+				  const struct intel_wait *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	bool first = false;
+
+	spin_lock(&b->lock);
+	if (b->first_waiter == wait->task)
+		first =__intel_breadcrumbs_enable_irq(b);
+	spin_unlock(&b->lock);
+
+	return first;
+}
+
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine)
+{
+	mod_timer(&engine->breadcrumbs.fake_irq, jiffies + 1);
+}
+
+static inline bool chain_wakeup(struct rb_node *rb, int priority)
+{
+	return rb && to_wait(rb)->task->prio <= priority;
+}
+
+void intel_engine_remove_wait(struct intel_engine_cs *engine,
+			      struct intel_wait *wait)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	/* Quick check to see if this waiter was already decoupled from
+	 * the tree by the bottom-half to avoid contention on the spinlock
+	 * by the herd.
+	 */
+	if (RB_EMPTY_NODE(&wait->node))
+		return;
+
+	spin_lock(&b->lock);
+
+	if (b->first_waiter == wait->task) {
+		struct rb_node *next;
+		struct task_struct *task;
+		const int priority = wait->task->prio;
+
+		/* We are the current bottom-half. Find the next candidate,
+		 * the first waiter in the queue on the remaining oldest
+		 * request. As multiple seqnos may complete in the time it
+		 * takes us to wake up and find the next waiter, we have to
+		 * wake up that waiter for it to perform its own coherent
+		 * completion check.
+		 */
+		next = rb_next(&wait->node);
+		if (chain_wakeup(next, priority)) {
+			/* If the next waiter is already complete,
+			 * wake it up and continue onto the next waiter. So
+			 * if have a small herd, they will wake up in parallel
+			 * rather than sequentially, which should reduce
+			 * the overall latency in waking all the completed
+			 * clients.
+			 *
+			 * However, waking up a chain adds extra latency to
+			 * the first_waiter. This is undesirable if that
+			 * waiter is a high priority task.
+			 */
+			u32 seqno = engine->get_seqno(engine, true);
+			while (i915_seqno_passed(seqno,
+						 to_wait(next)->seqno)) {
+				struct rb_node *n = rb_next(next);
+				__intel_breadcrumbs_finish(b, to_wait(next));
+				next = n;
+				if (!chain_wakeup(next, priority))
+					break;
+			}
+		}
+		task = next ? to_wait(next)->task : NULL;
+
+		smp_store_mb(b->first_waiter, task);
+		if (task) {
+			/* In our haste, we may have completed the first waiter
+			 * before we enabled the interrupt. Do so now as we
+			 * have a second waiter for a future seqno. Afterwards,
+			 * we have to wake up that waiter in case we missed
+			 * the interrupt, or if we have to handle an
+			 * exception rather than a seqno completion.
+			 */
+			if (to_wait(next)->seqno != wait->seqno)
+				__intel_breadcrumbs_enable_irq(b);
+			wake_up_process(task);
+		} else
+			__intel_breadcrumbs_disable_irq(b);
+	}
+
+	if (!RB_EMPTY_NODE(&wait->node))
+		rb_erase(&wait->node, &b->waiters);
+	spin_unlock(&b->lock);
+}
+
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	spin_lock_init(&b->lock);
+	setup_timer(&b->fake_irq,
+		    intel_breadcrumbs_fake_irq,
+		    (unsigned long)engine);
+}
+
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
+{
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+
+	del_timer_sync(&b->fake_irq);
+}
+
+void intel_kick_waiters(struct drm_i915_private *i915)
+{
+	struct intel_engine_cs *engine;
+	int i;
+
+	/* To avoid the task_struct disappearing beneath us as we wake up
+	 * the process, we must first inspect the task_struct->state under the
+	 * RCU lock, i.e. as we call wake_up_process() we must be holding the
+	 * rcu_read_lock().
+	 */
+	rcu_read_lock();
+	for_each_ring(engine, i915, i)
+		intel_engine_wakeup(engine);
+	rcu_read_unlock();
+}
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 44d792d76e6f..0f8780f94b8c 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1898,6 +1898,8 @@ void intel_logical_ring_cleanup(struct intel_engine_cs *ring)
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
 
+	intel_engine_fini_breadcrumbs(ring);
+
 	if (ring->status_page.obj) {
 		kunmap(sg_page(ring->status_page.obj->pages->sgl));
 		ring->status_page.obj = NULL;
@@ -1915,10 +1917,11 @@ static int logical_ring_init(struct drm_device *dev, struct intel_engine_cs *rin
 	ring->buffer = NULL;
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	INIT_LIST_HEAD(&ring->buffers);
 	INIT_LIST_HEAD(&ring->execlist_queue);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index a1d43b2c7077..60b0df2c5399 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2152,6 +2152,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	WARN_ON(ring->buffer);
 
 	ring->dev = dev;
+	ring->i915 = to_i915(dev);
 	INIT_LIST_HEAD(&ring->active_list);
 	INIT_LIST_HEAD(&ring->request_list);
 	INIT_LIST_HEAD(&ring->execlist_queue);
@@ -2159,7 +2160,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
 	i915_gem_batch_pool_init(dev, &ring->batch_pool);
 	memset(ring->semaphore.sync_seqno, 0, sizeof(ring->semaphore.sync_seqno));
 
-	init_waitqueue_head(&ring->irq_queue);
+	intel_engine_init_breadcrumbs(ring);
 
 	ringbuf = intel_engine_create_ringbuffer(ring, 32 * PAGE_SIZE);
 	if (IS_ERR(ringbuf)) {
@@ -2223,6 +2224,8 @@ void intel_cleanup_ring_buffer(struct intel_engine_cs *ring)
 
 	i915_cmd_parser_fini_ring(ring);
 	i915_gem_batch_pool_fini(&ring->batch_pool);
+	intel_engine_fini_breadcrumbs(ring);
+
 	ring->dev = NULL;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 49574ffe54bc..c5564070d656 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -157,9 +157,35 @@ struct  intel_engine_cs {
 #define LAST_USER_RING (VECS + 1)
 	u32		mmio_base;
 	struct		drm_device *dev;
+	struct drm_i915_private *i915;
 	struct intel_ringbuffer *buffer;
 	struct list_head buffers;
 
+	/* Rather than have every client wait upon all user interrupts,
+	 * with the herd waking after every interrupt and each doing the
+	 * heavyweight seqno dance, we delegate the task (of being the
+	 * bottom-half of the user interrupt) to the first client. After
+	 * every interrupt, we wake up one client, who does the heavyweight
+	 * coherent seqno read and either goes back to sleep (if incomplete),
+	 * or wakes up all the completed clients in parallel, before then
+	 * transferring the bottom-half status to the next client in the queue.
+	 *
+	 * Compared to walking the entire list of waiters in a single dedicated
+	 * bottom-half, we reduce the latency of the first waiter by avoiding
+	 * a context switch, but incur additional coherent seqno reads when
+	 * following the chain of request breadcrumbs. Since it is most likely
+	 * that we have a single client waiting on each seqno, then reducing
+	 * the overhead of waking that client is much preferred.
+	 */
+	struct intel_breadcrumbs {
+		spinlock_t lock; /* protects the lists of requests */
+		struct rb_root waiters; /* sorted by retirement, priority */
+		struct task_struct *first_waiter; /* bh for user interrupts */
+		struct timer_list fake_irq; /* used after a missed interrupt */
+		bool irq_enabled;
+		bool rpm_wakelock;
+	} breadcrumbs;
+
 	/*
 	 * A pool of objects to use as shadow copies of client batch buffers
 	 * when the command parser is enabled. Prevents the client from
@@ -303,8 +329,6 @@ struct  intel_engine_cs {
 
 	bool gpu_caches_dirty;
 
-	wait_queue_head_t irq_queue;
-
 	struct intel_context *default_context;
 	struct intel_context *last_context;
 
@@ -510,4 +534,45 @@ void intel_ring_reserved_space_end(struct intel_ringbuffer *ringbuf);
 /* Legacy ringbuffer specific portion of reservation code: */
 int intel_ring_reserve_space(struct drm_i915_gem_request *request);
 
+/* intel_breadcrumbs.c -- user interrupt bottom-half for waiters */
+struct intel_wait {
+	struct rb_node node;
+	struct task_struct *task;
+	u32 seqno;
+};
+void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine);
+static inline void intel_wait_init(struct intel_wait *wait, u32 seqno)
+{
+	wait->task = current;
+	wait->seqno = seqno;
+}
+static inline bool intel_wait_complete(const struct intel_wait *wait)
+{
+	return RB_EMPTY_NODE(&wait->node);
+}
+bool intel_engine_add_wait(struct intel_engine_cs *engine,
+			   struct intel_wait *wait);
+bool intel_engine_enable_wait_irq(struct intel_engine_cs *engine,
+				  const struct intel_wait *wait);
+void intel_engine_remove_wait(struct intel_engine_cs *engine,
+			      struct intel_wait *wait);
+static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
+{
+	return READ_ONCE(engine->breadcrumbs.first_waiter);
+}
+static inline bool intel_engine_wakeup(struct intel_engine_cs *engine)
+{
+	struct task_struct *task = READ_ONCE(engine->breadcrumbs.first_waiter);
+	/* Note that for this not to dangerously chase a dangling pointer,
+	 * the caller is responsible for ensure that the task remain valid for
+	 * wake_up_process() i.e. that the RCU grace period cannot expire.
+	 */
+	if (task)
+		wake_up_process(task);
+	return task != NULL;
+}
+void intel_engine_enable_fake_irq(struct intel_engine_cs *engine);
+void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine);
+void intel_kick_waiters(struct drm_i915_private *i915);
+
 #endif /* _INTEL_RINGBUFFER_H_ */
-- 
2.6.4

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 16/32] drm/i915: Separate out the seqno-barrier from engine->get_seqno

[Chris Wilson]

In order to simplify the next couple of patches, extract the
lazy_coherency optimisation our of the engine->get_seqno() vfunc into
its own callback.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c      |  6 ++---
 drivers/gpu/drm/i915/i915_drv.h          | 12 ++++++----
 drivers/gpu/drm/i915/i915_gpu_error.c    |  2 +-
 drivers/gpu/drm/i915/i915_irq.c          |  4 ++--
 drivers/gpu/drm/i915/i915_trace.h        |  2 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c |  4 ++--
 drivers/gpu/drm/i915/intel_lrc.c         | 39 ++++++++++++--------------------
 drivers/gpu/drm/i915/intel_ringbuffer.c  | 36 +++++++++++++++--------------
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  4 ++--
 9 files changed, 53 insertions(+), 56 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 48e574247a30..6344fe69ab82 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -600,7 +600,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
 					   ring->name,
 					   i915_gem_request_get_seqno(work->flip_queued_req),
 					   dev_priv->next_seqno,
-					   ring->get_seqno(ring, true),
+					   ring->get_seqno(ring),
 					   i915_gem_request_completed(work->flip_queued_req, true));
 			} else
 				seq_printf(m, "Flip not associated with any ring\n");
@@ -734,7 +734,7 @@ static void i915_ring_seqno_info(struct seq_file *m,
 
 	if (ring->get_seqno) {
 		seq_printf(m, "Current sequence (%s): %x\n",
-			   ring->name, ring->get_seqno(ring, false));
+			   ring->name, ring->get_seqno(ring));
 	}
 
 	spin_lock(&ring->breadcrumbs.lock);
@@ -1353,7 +1353,7 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 	intel_runtime_pm_get(dev_priv);
 
 	for_each_ring(ring, dev_priv, i) {
-		seqno[i] = ring->get_seqno(ring, false);
+		seqno[i] = ring->get_seqno(ring);
 		acthd[i] = intel_ring_get_active_head(ring);
 	}
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 830d760aa562..ff83f148658f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2981,15 +2981,19 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
 static inline bool i915_gem_request_started(struct drm_i915_gem_request *req,
 					   bool lazy_coherency)
 {
-	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
-	return i915_seqno_passed(seqno, req->previous_seqno);
+	if (!lazy_coherency && req->ring->seqno_barrier)
+		req->ring->seqno_barrier(req->ring);
+	return i915_seqno_passed(req->ring->get_seqno(req->ring),
+				 req->previous_seqno);
 }
 
 static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
 					      bool lazy_coherency)
 {
-	u32 seqno = req->ring->get_seqno(req->ring, lazy_coherency);
-	return i915_seqno_passed(seqno, req->seqno);
+	if (!lazy_coherency && req->ring->seqno_barrier)
+		req->ring->seqno_barrier(req->ring);
+	return i915_seqno_passed(req->ring->get_seqno(req->ring),
+				 req->seqno);
 }
 
 int __must_check i915_gem_get_seqno(struct drm_device *dev, u32 *seqno);
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index f805d117f3d1..01d0206ca4dd 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -902,8 +902,8 @@ static void i915_record_ring_state(struct drm_device *dev,
 
 	ering->waiting = intel_engine_has_waiter(ring);
 	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
-	ering->seqno = ring->get_seqno(ring, false);
 	ering->acthd = intel_ring_get_active_head(ring);
+	ering->seqno = ring->get_seqno(ring);
 	ering->start = I915_READ_START(ring);
 	ering->head = I915_READ_HEAD(ring);
 	ering->tail = I915_READ_TAIL(ring);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index d250b4721a6a..da3c8aaa50a3 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2875,7 +2875,7 @@ static int semaphore_passed(struct intel_engine_cs *ring)
 	if (signaller->hangcheck.deadlock >= I915_NUM_RINGS)
 		return -1;
 
-	if (i915_seqno_passed(signaller->get_seqno(signaller, false), seqno))
+	if (i915_seqno_passed(signaller->get_seqno(signaller), seqno))
 		return 1;
 
 	/* cursory check for an unkickable deadlock */
@@ -2978,8 +2978,8 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 		semaphore_clear_deadlocks(dev_priv);
 
-		seqno = ring->get_seqno(ring, false);
 		acthd = intel_ring_get_active_head(ring);
+		seqno = ring->get_seqno(ring);
 
 		if (ring->hangcheck.seqno == seqno) {
 			if (ring_idle(ring, seqno)) {
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index 52b2d409945d..cfb5f78a6e84 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -573,7 +573,7 @@ TRACE_EVENT(i915_gem_request_notify,
 	    TP_fast_assign(
 			   __entry->dev = ring->dev->primary->index;
 			   __entry->ring = ring->id;
-			   __entry->seqno = ring->get_seqno(ring, false);
+			   __entry->seqno = ring->get_seqno(ring);
 			   ),
 
 	    TP_printk("dev=%u, ring=%u, seqno=%u",
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index a9a199bca2c2..740f10fa6331 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -112,7 +112,7 @@ bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
 				 struct intel_breadcrumb *wait)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
-	u32 seqno = engine->get_seqno(engine, true);
+	u32 seqno = engine->get_seqno(engine);
 	struct rb_node **p, *parent, *completed;
 	bool first;
 
@@ -222,7 +222,7 @@ void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
 			 * the overall latency in waking all the completed
 			 * clients.
 			 */
-			u32 seqno = engine->get_seqno(engine, true);
+			u32 seqno = engine->get_seqno(engine);
 			while (i915_seqno_passed(seqno,
 						 to_crumb(next)->seqno)) {
 				struct rb_node *n = rb_next(next);
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 780aa6d390aa..4e28f0b28f81 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1745,7 +1745,7 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
 	return 0;
 }
 
-static u32 gen8_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
+static u32 gen8_get_seqno(struct intel_engine_cs *ring)
 {
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
 }
@@ -1755,9 +1755,8 @@ static void gen8_set_seqno(struct intel_engine_cs *ring, u32 seqno)
 	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);
 }
 
-static u32 bxt_a_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
+static void bxt_seqno_barrier(struct intel_engine_cs *ring)
 {
-
 	/*
 	 * On BXT A steppings there is a HW coherency issue whereby the
 	 * MI_STORE_DATA_IMM storing the completed request's seqno
@@ -1768,11 +1767,7 @@ static u32 bxt_a_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
 	 * bxt_a_set_seqno(), where we also do a clflush after the write. So
 	 * this clflush in practice becomes an invalidate operation.
 	 */
-
-	if (!lazy_coherency)
-		intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
-
-	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
+	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
 static void bxt_a_set_seqno(struct intel_engine_cs *ring, u32 seqno)
@@ -1977,12 +1972,11 @@ static int logical_render_ring_init(struct drm_device *dev)
 		ring->init_hw = gen8_init_render_ring;
 	ring->init_context = gen8_init_rcs_context;
 	ring->cleanup = intel_fini_pipe_control;
+	ring->get_seqno = gen8_get_seqno;
+	ring->set_seqno = gen8_set_seqno;
 	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
-		ring->get_seqno = bxt_a_get_seqno;
+		ring->seqno_barrier = bxt_seqno_barrier;
 		ring->set_seqno = bxt_a_set_seqno;
-	} else {
-		ring->get_seqno = gen8_get_seqno;
-		ring->set_seqno = gen8_set_seqno;
 	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush_render;
@@ -2029,12 +2023,11 @@ static int logical_bsd_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS1_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
+	ring->get_seqno = gen8_get_seqno;
+	ring->set_seqno = gen8_set_seqno;
 	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
-		ring->get_seqno = bxt_a_get_seqno;
+		ring->seqno_barrier = bxt_seqno_barrier;
 		ring->set_seqno = bxt_a_set_seqno;
-	} else {
-		ring->get_seqno = gen8_get_seqno;
-		ring->set_seqno = gen8_set_seqno;
 	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
@@ -2084,12 +2077,11 @@ static int logical_blt_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_BCS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
+	ring->get_seqno = gen8_get_seqno;
+	ring->set_seqno = gen8_set_seqno;
 	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
-		ring->get_seqno = bxt_a_get_seqno;
+		ring->seqno_barrier = bxt_seqno_barrier;
 		ring->set_seqno = bxt_a_set_seqno;
-	} else {
-		ring->get_seqno = gen8_get_seqno;
-		ring->set_seqno = gen8_set_seqno;
 	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
@@ -2114,12 +2106,11 @@ static int logical_vebox_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VECS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
+	ring->get_seqno = gen8_get_seqno;
+	ring->set_seqno = gen8_set_seqno;
 	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
-		ring->get_seqno = bxt_a_get_seqno;
+		ring->seqno_barrier = bxt_seqno_barrier;
 		ring->set_seqno = bxt_a_set_seqno;
-	} else {
-		ring->get_seqno = gen8_get_seqno;
-		ring->set_seqno = gen8_set_seqno;
 	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index e90c28e2da31..3cd586eb24ba 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1485,8 +1485,8 @@ pc_render_add_request(struct drm_i915_gem_request *req)
 	return 0;
 }
 
-static u32
-gen6_ring_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
+static void
+gen6_seqno_barrier(struct intel_engine_cs *ring)
 {
 	/* Workaround to force correct ordering between irq and seqno writes on
 	 * ivb (and maybe also on snb) by reading from a CS register (like
@@ -1500,18 +1500,14 @@ gen6_ring_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
 	 * a delay after every batch i.e. much more frequent than a delay
 	 * when waiting for the interrupt (with the same net latency).
 	 */
-	if (!lazy_coherency) {
-		struct drm_i915_private *dev_priv = ring->dev->dev_private;
-		POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
-
-		intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
-	}
+	struct drm_i915_private *dev_priv = ring->i915;
+	POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
 
-	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
+	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
 static u32
-ring_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
+ring_get_seqno(struct intel_engine_cs *ring)
 {
 	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
 }
@@ -1523,7 +1519,7 @@ ring_set_seqno(struct intel_engine_cs *ring, u32 seqno)
 }
 
 static u32
-pc_render_get_seqno(struct intel_engine_cs *ring, bool lazy_coherency)
+pc_render_get_seqno(struct intel_engine_cs *ring)
 {
 	return ring->scratch.cpu_page[0];
 }
@@ -2698,7 +2694,8 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->irq_get = gen8_ring_get_irq;
 		ring->irq_put = gen8_ring_put_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
-		ring->get_seqno = gen6_ring_get_seqno;
+		ring->seqno_barrier = gen6_seqno_barrier;
+		ring->get_seqno = ring_get_seqno;
 		ring->set_seqno = ring_set_seqno;
 		if (i915_semaphore_is_enabled(dev)) {
 			WARN_ON(!dev_priv->semaphore_obj);
@@ -2715,7 +2712,8 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->irq_get = gen6_ring_get_irq;
 		ring->irq_put = gen6_ring_put_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
-		ring->get_seqno = gen6_ring_get_seqno;
+		ring->seqno_barrier = gen6_seqno_barrier;
+		ring->get_seqno = ring_get_seqno;
 		ring->set_seqno = ring_set_seqno;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.sync_to = gen6_ring_sync;
@@ -2829,7 +2827,8 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 			ring->write_tail = gen6_bsd_ring_write_tail;
 		ring->flush = gen6_bsd_ring_flush;
 		ring->add_request = gen6_add_request;
-		ring->get_seqno = gen6_ring_get_seqno;
+		ring->seqno_barrier = gen6_seqno_barrier;
+		ring->get_seqno = ring_get_seqno;
 		ring->set_seqno = ring_set_seqno;
 		if (INTEL_INFO(dev)->gen >= 8) {
 			ring->irq_enable_mask =
@@ -2901,7 +2900,8 @@ int intel_init_bsd2_ring_buffer(struct drm_device *dev)
 	ring->mmio_base = GEN8_BSD2_RING_BASE;
 	ring->flush = gen6_bsd_ring_flush;
 	ring->add_request = gen6_add_request;
-	ring->get_seqno = gen6_ring_get_seqno;
+	ring->seqno_barrier = gen6_seqno_barrier;
+	ring->get_seqno = ring_get_seqno;
 	ring->set_seqno = ring_set_seqno;
 	ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_VCS2_IRQ_SHIFT;
@@ -2931,7 +2931,8 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
 	ring->write_tail = ring_write_tail;
 	ring->flush = gen6_ring_flush;
 	ring->add_request = gen6_add_request;
-	ring->get_seqno = gen6_ring_get_seqno;
+	ring->seqno_barrier = gen6_seqno_barrier;
+	ring->get_seqno = ring_get_seqno;
 	ring->set_seqno = ring_set_seqno;
 	if (INTEL_INFO(dev)->gen >= 8) {
 		ring->irq_enable_mask =
@@ -2988,7 +2989,8 @@ int intel_init_vebox_ring_buffer(struct drm_device *dev)
 	ring->write_tail = ring_write_tail;
 	ring->flush = gen6_ring_flush;
 	ring->add_request = gen6_add_request;
-	ring->get_seqno = gen6_ring_get_seqno;
+	ring->seqno_barrier = gen6_seqno_barrier;
+	ring->get_seqno = ring_get_seqno;
 	ring->set_seqno = ring_set_seqno;
 
 	if (INTEL_INFO(dev)->gen >= 8) {
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 281ed2c92b91..2c2454ccdd96 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -218,8 +218,8 @@ struct  intel_engine_cs {
 	 * seen value is good enough. Note that the seqno will always be
 	 * monotonic, even if not coherent.
 	 */
-	u32		(*get_seqno)(struct intel_engine_cs *ring,
-				     bool lazy_coherency);
+	void		(*seqno_barrier)(struct intel_engine_cs *ring);
+	u32		(*get_seqno)(struct intel_engine_cs *ring);
 	void		(*set_seqno)(struct intel_engine_cs *ring,
 				     u32 seqno);
 	int		(*dispatch_execbuffer)(struct drm_i915_gem_request *req,
-- 
2.6.3

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Chris Wilson]

Now that we have split out the seqno-barrier from the
engine->get_seqno() callback itself, we can move the users of the
seqno-barrier to the required callsites simplifying the common code and
making the required workaround handling much more explicit.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c  |  4 ++--
 drivers/gpu/drm/i915/i915_drv.h      | 10 ++--------
 drivers/gpu/drm/i915/i915_gem.c      | 24 +++++++++++++++---------
 drivers/gpu/drm/i915/intel_display.c |  2 +-
 drivers/gpu/drm/i915/intel_pm.c      |  4 ++--
 5 files changed, 22 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 6344fe69ab82..8860dec36aae 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -601,7 +601,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
 					   i915_gem_request_get_seqno(work->flip_queued_req),
 					   dev_priv->next_seqno,
 					   ring->get_seqno(ring),
-					   i915_gem_request_completed(work->flip_queued_req, true));
+					   i915_gem_request_completed(work->flip_queued_req));
 			} else
 				seq_printf(m, "Flip not associated with any ring\n");
 			seq_printf(m, "Flip queued on frame %d, (was ready on frame %d), now %d\n",
@@ -1353,8 +1353,8 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 	intel_runtime_pm_get(dev_priv);
 
 	for_each_ring(ring, dev_priv, i) {
-		seqno[i] = ring->get_seqno(ring);
 		acthd[i] = intel_ring_get_active_head(ring);
+		seqno[i] = ring->get_seqno(ring);
 	}
 
 	intel_runtime_pm_put(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index ff83f148658f..d099e960f9b8 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2978,20 +2978,14 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
 	return (int32_t)(seq1 - seq2) >= 0;
 }
 
-static inline bool i915_gem_request_started(struct drm_i915_gem_request *req,
-					   bool lazy_coherency)
+static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
 {
-	if (!lazy_coherency && req->ring->seqno_barrier)
-		req->ring->seqno_barrier(req->ring);
 	return i915_seqno_passed(req->ring->get_seqno(req->ring),
 				 req->previous_seqno);
 }
 
-static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
-					      bool lazy_coherency)
+static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
 {
-	if (!lazy_coherency && req->ring->seqno_barrier)
-		req->ring->seqno_barrier(req->ring);
 	return i915_seqno_passed(req->ring->get_seqno(req->ring),
 				 req->seqno);
 }
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fa0cf6c9f4d0..f3c1e268f614 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1173,12 +1173,12 @@ static bool __i915_spin_request(struct drm_i915_gem_request *req,
 	 */
 
 	/* Only spin if we know the GPU is processing this request */
-	if (!i915_gem_request_started(req, true))
+	if (!i915_gem_request_started(req))
 		return false;
 
 	timeout = local_clock_us(&cpu) + 5;
 	do {
-		if (i915_gem_request_completed(req, true))
+		if (i915_gem_request_completed(req))
 			return true;
 
 		if (signal_pending_state(state, wait->task))
@@ -1230,7 +1230,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	if (list_empty(&req->list))
 		return 0;
 
-	if (i915_gem_request_completed(req, true))
+	if (i915_gem_request_completed(req))
 		return 0;
 
 	timeout_remain = MAX_SCHEDULE_TIMEOUT;
@@ -1299,7 +1299,10 @@ wakeup:		set_task_state(wait.task, state);
 		 * but it is easier and safer to do it every time the waiter
 		 * is woken.
 		 */
-		if (i915_gem_request_completed(req, false))
+		if (req->ring->seqno_barrier)
+			req->ring->seqno_barrier(req->ring);
+
+		if (i915_gem_request_completed(req))
 			break;
 
 		/* We need to check whether any gpu reset happened in between
@@ -2731,8 +2734,11 @@ i915_gem_find_active_request(struct intel_engine_cs *ring)
 {
 	struct drm_i915_gem_request *request;
 
+	if (ring->seqno_barrier)
+		ring->seqno_barrier(ring);
+
 	list_for_each_entry(request, &ring->request_list, list) {
-		if (i915_gem_request_completed(request, false))
+		if (i915_gem_request_completed(request))
 			continue;
 
 		return request;
@@ -2873,7 +2879,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 					   struct drm_i915_gem_request,
 					   list);
 
-		if (!i915_gem_request_completed(request, true))
+		if (!i915_gem_request_completed(request))
 			break;
 
 		i915_gem_request_retire(request);
@@ -2897,7 +2903,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 	}
 
 	if (unlikely(ring->trace_irq_req &&
-		     i915_gem_request_completed(ring->trace_irq_req, true))) {
+		     i915_gem_request_completed(ring->trace_irq_req))) {
 		ring->irq_put(ring);
 		i915_gem_request_assign(&ring->trace_irq_req, NULL);
 	}
@@ -3007,7 +3013,7 @@ i915_gem_object_flush_active(struct drm_i915_gem_object *obj)
 		if (list_empty(&req->list))
 			goto retire;
 
-		if (i915_gem_request_completed(req, true)) {
+		if (i915_gem_request_completed(req)) {
 			__i915_gem_request_retire__upto(req);
 retire:
 			i915_gem_object_retire__read(obj, i);
@@ -3116,7 +3122,7 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
 	if (to == from)
 		return 0;
 
-	if (i915_gem_request_completed(from_req, true))
+	if (i915_gem_request_completed(from_req))
 		return 0;
 
 	if (!i915_semaphore_is_enabled(obj->base.dev)) {
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 875bdf814d73..ffcdc2c631e1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11459,7 +11459,7 @@ static bool __intel_pageflip_stall_check(struct drm_device *dev,
 
 	if (work->flip_ready_vblank == 0) {
 		if (work->flip_queued_req &&
-		    !i915_gem_request_completed(work->flip_queued_req, true))
+		    !i915_gem_request_completed(work->flip_queued_req))
 			return false;
 
 		work->flip_ready_vblank = drm_crtc_vblank_count(crtc);
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 99f2642fd5df..570628628a90 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7188,7 +7188,7 @@ static void __intel_rps_boost_work(struct work_struct *work)
 	struct request_boost *boost = container_of(work, struct request_boost, work);
 	struct drm_i915_gem_request *req = boost->req;
 
-	if (!i915_gem_request_completed(req, true))
+	if (!i915_gem_request_completed(req))
 		gen6_rps_boost(to_i915(req->ring->dev), NULL,
 			       req->emitted_jiffies);
 
@@ -7204,7 +7204,7 @@ void intel_queue_rps_boost_for_request(struct drm_device *dev,
 	if (req == NULL || INTEL_INFO(dev)->gen < 6)
 		return;
 
-	if (i915_gem_request_completed(req, true))
+	if (i915_gem_request_completed(req))
 		return;
 
 	boost = kmalloc(sizeof(*boost), GFP_ATOMIC);
-- 
2.6.3

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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Tvrtko Ursulin]

Hi,

On 11/12/15 11:33, Chris Wilson wrote:
> Now that we have split out the seqno-barrier from the
> engine->get_seqno() callback itself, we can move the users of the
> seqno-barrier to the required callsites simplifying the common code and
> making the required workaround handling much more explicit.

What bothers me about this patch, and the one preceding it, is that I 
don't see a tangible improvement for the programmer who still has to 
know when to read the seqno and when to "read it harder, read for real".

Barrier in this sense has a relation to the state of things but somehow 
feels too low level to me when used from the code. But to be fair I am 
not sure how to better define it.

Would ring->get_seqno paired with ring->read_seqno perhaps make sense? 
Implementation for ring->read_seqno would just be a flush followed by 
ring->get_seqno then. Or maybe keep the barrier and add ring->read_seqno 
which would be ring->seqno_barrier + ring_get_seqno?

Regards,

Tvrtko

>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c  |  4 ++--
>   drivers/gpu/drm/i915/i915_drv.h      | 10 ++--------
>   drivers/gpu/drm/i915/i915_gem.c      | 24 +++++++++++++++---------
>   drivers/gpu/drm/i915/intel_display.c |  2 +-
>   drivers/gpu/drm/i915/intel_pm.c      |  4 ++--
>   5 files changed, 22 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 6344fe69ab82..8860dec36aae 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -601,7 +601,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
>   					   i915_gem_request_get_seqno(work->flip_queued_req),
>   					   dev_priv->next_seqno,
>   					   ring->get_seqno(ring),
> -					   i915_gem_request_completed(work->flip_queued_req, true));
> +					   i915_gem_request_completed(work->flip_queued_req));
>   			} else
>   				seq_printf(m, "Flip not associated with any ring\n");
>   			seq_printf(m, "Flip queued on frame %d, (was ready on frame %d), now %d\n",
> @@ -1353,8 +1353,8 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
>   	intel_runtime_pm_get(dev_priv);
>
>   	for_each_ring(ring, dev_priv, i) {
> -		seqno[i] = ring->get_seqno(ring);
>   		acthd[i] = intel_ring_get_active_head(ring);
> +		seqno[i] = ring->get_seqno(ring);
>   	}
>
>   	intel_runtime_pm_put(dev_priv);
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index ff83f148658f..d099e960f9b8 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2978,20 +2978,14 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
>   	return (int32_t)(seq1 - seq2) >= 0;
>   }
>
> -static inline bool i915_gem_request_started(struct drm_i915_gem_request *req,
> -					   bool lazy_coherency)
> +static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
>   {
> -	if (!lazy_coherency && req->ring->seqno_barrier)
> -		req->ring->seqno_barrier(req->ring);
>   	return i915_seqno_passed(req->ring->get_seqno(req->ring),
>   				 req->previous_seqno);
>   }
>
> -static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
> -					      bool lazy_coherency)
> +static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
>   {
> -	if (!lazy_coherency && req->ring->seqno_barrier)
> -		req->ring->seqno_barrier(req->ring);
>   	return i915_seqno_passed(req->ring->get_seqno(req->ring),
>   				 req->seqno);
>   }
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index fa0cf6c9f4d0..f3c1e268f614 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1173,12 +1173,12 @@ static bool __i915_spin_request(struct drm_i915_gem_request *req,
>   	 */
>
>   	/* Only spin if we know the GPU is processing this request */
> -	if (!i915_gem_request_started(req, true))
> +	if (!i915_gem_request_started(req))
>   		return false;
>
>   	timeout = local_clock_us(&cpu) + 5;
>   	do {
> -		if (i915_gem_request_completed(req, true))
> +		if (i915_gem_request_completed(req))
>   			return true;
>
>   		if (signal_pending_state(state, wait->task))
> @@ -1230,7 +1230,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
>   	if (list_empty(&req->list))
>   		return 0;
>
> -	if (i915_gem_request_completed(req, true))
> +	if (i915_gem_request_completed(req))
>   		return 0;
>
>   	timeout_remain = MAX_SCHEDULE_TIMEOUT;
> @@ -1299,7 +1299,10 @@ wakeup:		set_task_state(wait.task, state);
>   		 * but it is easier and safer to do it every time the waiter
>   		 * is woken.
>   		 */
> -		if (i915_gem_request_completed(req, false))
> +		if (req->ring->seqno_barrier)
> +			req->ring->seqno_barrier(req->ring);
> +
> +		if (i915_gem_request_completed(req))
>   			break;
>
>   		/* We need to check whether any gpu reset happened in between
> @@ -2731,8 +2734,11 @@ i915_gem_find_active_request(struct intel_engine_cs *ring)
>   {
>   	struct drm_i915_gem_request *request;
>
> +	if (ring->seqno_barrier)
> +		ring->seqno_barrier(ring);
> +
>   	list_for_each_entry(request, &ring->request_list, list) {
> -		if (i915_gem_request_completed(request, false))
> +		if (i915_gem_request_completed(request))
>   			continue;
>
>   		return request;
> @@ -2873,7 +2879,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
>   					   struct drm_i915_gem_request,
>   					   list);
>
> -		if (!i915_gem_request_completed(request, true))
> +		if (!i915_gem_request_completed(request))
>   			break;
>
>   		i915_gem_request_retire(request);
> @@ -2897,7 +2903,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
>   	}
>
>   	if (unlikely(ring->trace_irq_req &&
> -		     i915_gem_request_completed(ring->trace_irq_req, true))) {
> +		     i915_gem_request_completed(ring->trace_irq_req))) {
>   		ring->irq_put(ring);
>   		i915_gem_request_assign(&ring->trace_irq_req, NULL);
>   	}
> @@ -3007,7 +3013,7 @@ i915_gem_object_flush_active(struct drm_i915_gem_object *obj)
>   		if (list_empty(&req->list))
>   			goto retire;
>
> -		if (i915_gem_request_completed(req, true)) {
> +		if (i915_gem_request_completed(req)) {
>   			__i915_gem_request_retire__upto(req);
>   retire:
>   			i915_gem_object_retire__read(obj, i);
> @@ -3116,7 +3122,7 @@ __i915_gem_object_sync(struct drm_i915_gem_object *obj,
>   	if (to == from)
>   		return 0;
>
> -	if (i915_gem_request_completed(from_req, true))
> +	if (i915_gem_request_completed(from_req))
>   		return 0;
>
>   	if (!i915_semaphore_is_enabled(obj->base.dev)) {
> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> index 875bdf814d73..ffcdc2c631e1 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -11459,7 +11459,7 @@ static bool __intel_pageflip_stall_check(struct drm_device *dev,
>
>   	if (work->flip_ready_vblank == 0) {
>   		if (work->flip_queued_req &&
> -		    !i915_gem_request_completed(work->flip_queued_req, true))
> +		    !i915_gem_request_completed(work->flip_queued_req))
>   			return false;
>
>   		work->flip_ready_vblank = drm_crtc_vblank_count(crtc);
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 99f2642fd5df..570628628a90 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -7188,7 +7188,7 @@ static void __intel_rps_boost_work(struct work_struct *work)
>   	struct request_boost *boost = container_of(work, struct request_boost, work);
>   	struct drm_i915_gem_request *req = boost->req;
>
> -	if (!i915_gem_request_completed(req, true))
> +	if (!i915_gem_request_completed(req))
>   		gen6_rps_boost(to_i915(req->ring->dev), NULL,
>   			       req->emitted_jiffies);
>
> @@ -7204,7 +7204,7 @@ void intel_queue_rps_boost_for_request(struct drm_device *dev,
>   	if (req == NULL || INTEL_INFO(dev)->gen < 6)
>   		return;
>
> -	if (i915_gem_request_completed(req, true))
> +	if (i915_gem_request_completed(req))
>   		return;
>
>   	boost = kmalloc(sizeof(*boost), GFP_ATOMIC);
>
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Chris Wilson]

On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
> 
> Hi,
> 
> On 11/12/15 11:33, Chris Wilson wrote:
> >Now that we have split out the seqno-barrier from the
> >engine->get_seqno() callback itself, we can move the users of the
> >seqno-barrier to the required callsites simplifying the common code and
> >making the required workaround handling much more explicit.
> 
> What bothers me about this patch, and the one preceding it, is that
> I don't see a tangible improvement for the programmer who still has
> to know when to read the seqno and when to "read it harder, read for
> real".

In earlier patches, I called it irq_barrier.

It's not reading it harder. It's just that there is a ordering issue
with receiving an interrupt and the seqno write being visible.

> Barrier in this sense has a relation to the state of things but
> somehow feels too low level to me when used from the code. But to be
> fair I am not sure how to better define it.
> 
> Would ring->get_seqno paired with ring->read_seqno perhaps make
> sense? Implementation for ring->read_seqno would just be a flush
> followed by ring->get_seqno then. Or maybe keep the barrier and add
> ring->read_seqno which would be ring->seqno_barrier +
> ring_get_seqno?

No.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Dave Gordon]

On 14/12/15 15:11, Chris Wilson wrote:
> On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
>>
>> Hi,
>>
>> On 11/12/15 11:33, Chris Wilson wrote:
>>> Now that we have split out the seqno-barrier from the
>>> engine->get_seqno() callback itself, we can move the users of the
>>> seqno-barrier to the required callsites simplifying the common code and
>>> making the required workaround handling much more explicit.
>>
>> What bothers me about this patch, and the one preceding it, is that
>> I don't see a tangible improvement for the programmer who still has
>> to know when to read the seqno and when to "read it harder, read for
>> real".
>
> In earlier patches, I called it irq_barrier.
>
> It's not reading it harder. It's just that there is a ordering issue
> with receiving an interrupt and the seqno write being visible.
>
>> Barrier in this sense has a relation to the state of things but
>> somehow feels too low level to me when used from the code. But to be
>> fair I am not sure how to better define it.
>>
>> Would ring->get_seqno paired with ring->read_seqno perhaps make
>> sense? Implementation for ring->read_seqno would just be a flush
>> followed by ring->get_seqno then. Or maybe keep the barrier and add
>> ring->read_seqno which would be ring->seqno_barrier +
>> ring_get_seqno?
>
> No.
> -Chris

We could instead put the knowledge about whether and how to read "for 
real" inside the read-the-seqno function. For example:

	struct intel_engine_cs {
		...
		u32 last_seqno_seen;
	}

	u32 intel_ring_read_seqno(struct intel_engine_cs *engine) {
		// First try simple read
		u32 seqno = intel_ring_get_seqno(engine);

		if (seqno == engine->last_seqno_seen) {
			// Do additional flush, then try again
			engine->seqno_barrier(engine);
			seqno = intel_ring_get_seqno(engine);
		}

		engine->last_seqno_seen = seqno;
		return seqno;
	}

Then callers don't have to know anything about coherency; they can just 
assume that they will automatically get the latest value.

In the presumably common case where the value *has* been updated, and 
the cache has noted the update and invalidated the old local value, the 
first read will successfully find the updated seqno and return quickly.

Then we only do the extra work in the case where there would otherwise 
appear to be nothing to do (i.e. when we would sleep, or spin, or 
otherwise wait, if this function were to return the same value as last 
time).

.Dave.
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Chris Wilson]

On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
> On 14/12/15 15:11, Chris Wilson wrote:
> >On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
> >>
> >>Hi,
> >>
> >>On 11/12/15 11:33, Chris Wilson wrote:
> >>>Now that we have split out the seqno-barrier from the
> >>>engine->get_seqno() callback itself, we can move the users of the
> >>>seqno-barrier to the required callsites simplifying the common code and
> >>>making the required workaround handling much more explicit.
> >>
> >>What bothers me about this patch, and the one preceding it, is that
> >>I don't see a tangible improvement for the programmer who still has
> >>to know when to read the seqno and when to "read it harder, read for
> >>real".
> >
> >In earlier patches, I called it irq_barrier.
> >
> >It's not reading it harder. It's just that there is a ordering issue
> >with receiving an interrupt and the seqno write being visible.
> >
> >>Barrier in this sense has a relation to the state of things but
> >>somehow feels too low level to me when used from the code. But to be
> >>fair I am not sure how to better define it.
> >>
> >>Would ring->get_seqno paired with ring->read_seqno perhaps make
> >>sense? Implementation for ring->read_seqno would just be a flush
> >>followed by ring->get_seqno then. Or maybe keep the barrier and add
> >>ring->read_seqno which would be ring->seqno_barrier +
> >>ring_get_seqno?
> >
> >No.
> >-Chris
> 
> We could instead put the knowledge about whether and how to read
> "for real" inside the read-the-seqno function. For example:

You do appreciate the irony that you are on the reviewer list for patches
that do that?

http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34

There is just one place that we need the extra work, after the
interrupt. All other places only care about the current value of the
seqno in the CPU cache.
-Chris

-- 
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Dave Gordon]

On 04/01/16 11:26, Chris Wilson wrote:
> On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
>> On 14/12/15 15:11, Chris Wilson wrote:
>>> On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
>>>>
>>>> Hi,
>>>>
>>>> On 11/12/15 11:33, Chris Wilson wrote:
>>>>> Now that we have split out the seqno-barrier from the
>>>>> engine->get_seqno() callback itself, we can move the users of the
>>>>> seqno-barrier to the required callsites simplifying the common code and
>>>>> making the required workaround handling much more explicit.
>>>>
>>>> What bothers me about this patch, and the one preceding it, is that
>>>> I don't see a tangible improvement for the programmer who still has
>>>> to know when to read the seqno and when to "read it harder, read for
>>>> real".
>>>
>>> In earlier patches, I called it irq_barrier.
>>>
>>> It's not reading it harder. It's just that there is a ordering issue
>>> with receiving an interrupt and the seqno write being visible.
>>>
>>>> Barrier in this sense has a relation to the state of things but
>>>> somehow feels too low level to me when used from the code. But to be
>>>> fair I am not sure how to better define it.
>>>>
>>>> Would ring->get_seqno paired with ring->read_seqno perhaps make
>>>> sense? Implementation for ring->read_seqno would just be a flush
>>>> followed by ring->get_seqno then. Or maybe keep the barrier and add
>>>> ring->read_seqno which would be ring->seqno_barrier +
>>>> ring_get_seqno?
>>>
>>> No.
>>> -Chris
>>
>> We could instead put the knowledge about whether and how to read
>> "for real" inside the read-the-seqno function. For example:
>
> You do appreciate the irony that you are on the reviewer list for patches
> that do that?
>
> http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34

No, I haven't got as far as that one, since it was posted over a week 
after the message at the head of this thread. Anyway, I still can't see 
in that patch anything equivalent to what I described above.

> There is just one place that we need the extra work, after the
> interrupt. All other places only care about the current value of the
> seqno in the CPU cache.
> -Chris

So, we could instead have a per-engine flag which says, interrupt has 
happened, next reader should expect an update (and try hard to see one)?

Flow would be:
     IRQ->handler
         sets flag, wakes first waiter, clears IRQs
     waiter wakes up
         reads seqno (read fn sees flag => coherent, clear flag if new)
         checks whether (only) its request is completed
             not complete: enable IRQ, sleep
             seqno match: dequeue request, enable IRQ, process completion
             match+: dequeue request, wake next, process completion

where 'process completion' involves updating the request state and 
waking all /additional/ waiters on the same request, whereas 'wake next' 
refers to threads waiting on the /next/ request.

Is that what your patch is trying to achieve? It's a bit hard to tell 
with the seqno-read-optimisation and irq-dispatch changes mixed in with 
the r-b-tree and all the other things in this sequence.

I think it would be easier to understand if some of the more obvious 
improvements (such as 18/32, 20/32, 24/32) were pushed in earlier, so 
that the code is as clear as possible before the patches that actually 
change the way things work are applied. And all the reset-related 
patches could be later, as that's an area with some subtlety to it.

.Dave.
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Chris Wilson]

On Mon, Jan 04, 2016 at 01:02:25PM +0000, Dave Gordon wrote:
> On 04/01/16 11:26, Chris Wilson wrote:
> >On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
> >>On 14/12/15 15:11, Chris Wilson wrote:
> >>>On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
> >>>>
> >>>>Hi,
> >>>>
> >>>>On 11/12/15 11:33, Chris Wilson wrote:
> >>>>>Now that we have split out the seqno-barrier from the
> >>>>>engine->get_seqno() callback itself, we can move the users of the
> >>>>>seqno-barrier to the required callsites simplifying the common code and
> >>>>>making the required workaround handling much more explicit.
> >>>>
> >>>>What bothers me about this patch, and the one preceding it, is that
> >>>>I don't see a tangible improvement for the programmer who still has
> >>>>to know when to read the seqno and when to "read it harder, read for
> >>>>real".
> >>>
> >>>In earlier patches, I called it irq_barrier.
> >>>
> >>>It's not reading it harder. It's just that there is a ordering issue
> >>>with receiving an interrupt and the seqno write being visible.
> >>>
> >>>>Barrier in this sense has a relation to the state of things but
> >>>>somehow feels too low level to me when used from the code. But to be
> >>>>fair I am not sure how to better define it.
> >>>>
> >>>>Would ring->get_seqno paired with ring->read_seqno perhaps make
> >>>>sense? Implementation for ring->read_seqno would just be a flush
> >>>>followed by ring->get_seqno then. Or maybe keep the barrier and add
> >>>>ring->read_seqno which would be ring->seqno_barrier +
> >>>>ring_get_seqno?
> >>>
> >>>No.
> >>>-Chris
> >>
> >>We could instead put the knowledge about whether and how to read
> >>"for real" inside the read-the-seqno function. For example:
> >
> >You do appreciate the irony that you are on the reviewer list for patches
> >that do that?
> >
> >http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34
> 
> No, I haven't got as far as that one, since it was posted over a
> week after the message at the head of this thread. Anyway, I still
> can't see in that patch anything equivalent to what I described
> above.
> 
> >There is just one place that we need the extra work, after the
> >interrupt. All other places only care about the current value of the
> >seqno in the CPU cache.
> >-Chris
> 
> So, we could instead have a per-engine flag which says, interrupt
> has happened, next reader should expect an update (and try hard to
> see one)?

Go back and read. That patch adds the commentary that should explain
what needs to be done and where, continue on in the series you can see
just that micro-optimisation along with the required barriers.
-Chris

-- 
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Dave Gordon]

On 04/01/16 13:02, Dave Gordon wrote:
> On 04/01/16 11:26, Chris Wilson wrote:
>> On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
>>> On 14/12/15 15:11, Chris Wilson wrote:
>>>> On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
>>>>>
>>>>> Hi,
>>>>>
>>>>> On 11/12/15 11:33, Chris Wilson wrote:
>>>>>> Now that we have split out the seqno-barrier from the
>>>>>> engine->get_seqno() callback itself, we can move the users of the
>>>>>> seqno-barrier to the required callsites simplifying the common
>>>>>> code and
>>>>>> making the required workaround handling much more explicit.
>>>>>
>>>>> What bothers me about this patch, and the one preceding it, is that
>>>>> I don't see a tangible improvement for the programmer who still has
>>>>> to know when to read the seqno and when to "read it harder, read for
>>>>> real".
>>>>
>>>> In earlier patches, I called it irq_barrier.
>>>>
>>>> It's not reading it harder. It's just that there is a ordering issue
>>>> with receiving an interrupt and the seqno write being visible.
>>>>
>>>>> Barrier in this sense has a relation to the state of things but
>>>>> somehow feels too low level to me when used from the code. But to be
>>>>> fair I am not sure how to better define it.
>>>>>
>>>>> Would ring->get_seqno paired with ring->read_seqno perhaps make
>>>>> sense? Implementation for ring->read_seqno would just be a flush
>>>>> followed by ring->get_seqno then. Or maybe keep the barrier and add
>>>>> ring->read_seqno which would be ring->seqno_barrier +
>>>>> ring_get_seqno?
>>>>
>>>> No.
>>>> -Chris
>>>
>>> We could instead put the knowledge about whether and how to read
>>> "for real" inside the read-the-seqno function. For example:
>>
>> You do appreciate the irony that you are on the reviewer list for patches
>> that do that?
>>
>> http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34
>
> No, I haven't got as far as that one, since it was posted over a week
> after the message at the head of this thread. Anyway, I still can't see
> in that patch anything equivalent to what I described above.

Oh, I spotted what you meant, but it's not in /that/ patch (which was a 
version of PATCH 15/32 (Slaughter the thundering i915_wait_request herd)
it's in PATCH 19/32 (Check the CPU cached value of seqno after waking 
the waiter).

Even so, it's not at the same level of code structure; I was suggesting 
pushing it all the way down, because __i915_wait_request() and/or 
i915_gem_request_completed() aren't the only functions that use it.

.Dave.
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Chris Wilson]

On Mon, Jan 04, 2016 at 02:09:53PM +0000, Dave Gordon wrote:
> On 04/01/16 13:02, Dave Gordon wrote:
> >On 04/01/16 11:26, Chris Wilson wrote:
> >>On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
> >>>On 14/12/15 15:11, Chris Wilson wrote:
> >>>>On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
> >>>>>
> >>>>>Hi,
> >>>>>
> >>>>>On 11/12/15 11:33, Chris Wilson wrote:
> >>>>>>Now that we have split out the seqno-barrier from the
> >>>>>>engine->get_seqno() callback itself, we can move the users of the
> >>>>>>seqno-barrier to the required callsites simplifying the common
> >>>>>>code and
> >>>>>>making the required workaround handling much more explicit.
> >>>>>
> >>>>>What bothers me about this patch, and the one preceding it, is that
> >>>>>I don't see a tangible improvement for the programmer who still has
> >>>>>to know when to read the seqno and when to "read it harder, read for
> >>>>>real".
> >>>>
> >>>>In earlier patches, I called it irq_barrier.
> >>>>
> >>>>It's not reading it harder. It's just that there is a ordering issue
> >>>>with receiving an interrupt and the seqno write being visible.
> >>>>
> >>>>>Barrier in this sense has a relation to the state of things but
> >>>>>somehow feels too low level to me when used from the code. But to be
> >>>>>fair I am not sure how to better define it.
> >>>>>
> >>>>>Would ring->get_seqno paired with ring->read_seqno perhaps make
> >>>>>sense? Implementation for ring->read_seqno would just be a flush
> >>>>>followed by ring->get_seqno then. Or maybe keep the barrier and add
> >>>>>ring->read_seqno which would be ring->seqno_barrier +
> >>>>>ring_get_seqno?
> >>>>
> >>>>No.
> >>>>-Chris
> >>>
> >>>We could instead put the knowledge about whether and how to read
> >>>"for real" inside the read-the-seqno function. For example:
> >>
> >>You do appreciate the irony that you are on the reviewer list for patches
> >>that do that?
> >>
> >>http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34
> >
> >No, I haven't got as far as that one, since it was posted over a week
> >after the message at the head of this thread. Anyway, I still can't see
> >in that patch anything equivalent to what I described above.
> 
> Oh, I spotted what you meant, but it's not in /that/ patch (which
> was a version of PATCH 15/32 (Slaughter the thundering
> i915_wait_request herd)
> it's in PATCH 19/32 (Check the CPU cached value of seqno after
> waking the waiter).
> 
> Even so, it's not at the same level of code structure; I was
> suggesting pushing it all the way down, because
> __i915_wait_request() and/or i915_gem_request_completed() aren't the
> only functions that use it.

No. I am arguing that there should be precisely one piece of code
responsible for seqno-vs-interrupt ordering. Everywhere else should not
have to worry about that interrupts may be asserted before the HWS write
is posted.
-Chris

-- 
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Re: [PATCH 17/32] drm/i915: Remove the lazy_coherency parameter from request-completed?

[Dave Gordon]

On 04/01/16 14:20, Chris Wilson wrote:
> On Mon, Jan 04, 2016 at 02:09:53PM +0000, Dave Gordon wrote:
>> On 04/01/16 13:02, Dave Gordon wrote:
>>> On 04/01/16 11:26, Chris Wilson wrote:
>>>> On Mon, Jan 04, 2016 at 11:16:04AM +0000, Dave Gordon wrote:
>>>>> On 14/12/15 15:11, Chris Wilson wrote:
>>>>>> On Mon, Dec 14, 2015 at 02:59:30PM +0000, Tvrtko Ursulin wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 11/12/15 11:33, Chris Wilson wrote:
>>>>>>>> Now that we have split out the seqno-barrier from the
>>>>>>>> engine->get_seqno() callback itself, we can move the users of the
>>>>>>>> seqno-barrier to the required callsites simplifying the common
>>>>>>>> code and
>>>>>>>> making the required workaround handling much more explicit.
>>>>>>>
>>>>>>> What bothers me about this patch, and the one preceding it, is that
>>>>>>> I don't see a tangible improvement for the programmer who still has
>>>>>>> to know when to read the seqno and when to "read it harder, read for
>>>>>>> real".
>>>>>>
>>>>>> In earlier patches, I called it irq_barrier.
>>>>>>
>>>>>> It's not reading it harder. It's just that there is a ordering issue
>>>>>> with receiving an interrupt and the seqno write being visible.
>>>>>>
>>>>>>> Barrier in this sense has a relation to the state of things but
>>>>>>> somehow feels too low level to me when used from the code. But to be
>>>>>>> fair I am not sure how to better define it.
>>>>>>>
>>>>>>> Would ring->get_seqno paired with ring->read_seqno perhaps make
>>>>>>> sense? Implementation for ring->read_seqno would just be a flush
>>>>>>> followed by ring->get_seqno then. Or maybe keep the barrier and add
>>>>>>> ring->read_seqno which would be ring->seqno_barrier +
>>>>>>> ring_get_seqno?
>>>>>>
>>>>>> No.
>>>>>> -Chris
>>>>>
>>>>> We could instead put the knowledge about whether and how to read
>>>>> "for real" inside the read-the-seqno function. For example:
>>>>
>>>> You do appreciate the irony that you are on the reviewer list for patches
>>>> that do that?
>>>>
>>>> http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=breadcrumbs&id=34409f2d965001d7d63f21a1c5339b07eed6af34
>>>
>>> No, I haven't got as far as that one, since it was posted over a week
>>> after the message at the head of this thread. Anyway, I still can't see
>>> in that patch anything equivalent to what I described above.
>>
>> Oh, I spotted what you meant, but it's not in /that/ patch
>> (which was a version of PATCH 15/32 "Slaughter the thundering
>> i915_wait_request herd") it's in PATCH 19/32 "Check the CPU
>> cached value of seqno after waking the waiter".
>>
>> Even so, it's not at the same level of code structure; I was
>> suggesting pushing it all the way down, because
>> __i915_wait_request() and/or i915_gem_request_completed() aren't the
>> only functions that use it.
>
> No. I am arguing that there should be precisely one piece of code
> responsible for seqno-vs-interrupt ordering. Everywhere else should not
> have to worry about that interrupts may be asserted before the HWS write
> is posted.
> -Chris

That's what /I/ said. So it should be inside the /lowest-level/ 
function, the one that hands back a h/w sequence number to other code 
that doesn't care how it was obtained; in other words, either 
intel_ring_get_seqno() or a wrapper round it that incorporates the 
check-and-flush, if you still want the option of looking only at the 
cached copy.

Whereas you put the read-barrier-read logic in __i915_wait_request() but 
that's too high a level, and I don't think that's the only caller where 
it could be advantageous to conditionally update the cached seqno from 
the HWSP; and the fact of reading the HWSP is hidden inside the call to 
i915_gem_request(), which is working at an entirely different level of 
abstraction.

.Dave.
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[PATCH 18/32] drm/i915: Use HWS for seqno tracking everywhere

[Chris Wilson]

By using the same address for storing the HWS on every platform, we can
remove the platform specific vfuncs and reduce the get-seqno routine to
a single read of a cached memory location.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c      | 10 ++--
 drivers/gpu/drm/i915/i915_drv.h          |  4 +-
 drivers/gpu/drm/i915/i915_gpu_error.c    |  2 +-
 drivers/gpu/drm/i915/i915_irq.c          |  4 +-
 drivers/gpu/drm/i915/i915_trace.h        |  2 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c |  4 +-
 drivers/gpu/drm/i915/intel_lrc.c         | 46 ++---------------
 drivers/gpu/drm/i915/intel_ringbuffer.c  | 86 ++++++++------------------------
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  7 +--
 9 files changed, 43 insertions(+), 122 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 8860dec36aae..a03ed9e38499 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -600,7 +600,7 @@ static int i915_gem_pageflip_info(struct seq_file *m, void *data)
 					   ring->name,
 					   i915_gem_request_get_seqno(work->flip_queued_req),
 					   dev_priv->next_seqno,
-					   ring->get_seqno(ring),
+					   intel_ring_get_seqno(ring),
 					   i915_gem_request_completed(work->flip_queued_req));
 			} else
 				seq_printf(m, "Flip not associated with any ring\n");
@@ -732,10 +732,8 @@ static void i915_ring_seqno_info(struct seq_file *m,
 {
 	struct rb_node *rb;
 
-	if (ring->get_seqno) {
-		seq_printf(m, "Current sequence (%s): %x\n",
-			   ring->name, ring->get_seqno(ring));
-	}
+	seq_printf(m, "Current sequence (%s): %x\n",
+		   ring->name, intel_ring_get_seqno(ring));
 
 	spin_lock(&ring->breadcrumbs.lock);
 	for (rb = rb_first(&ring->breadcrumbs.requests);
@@ -1354,7 +1352,7 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 
 	for_each_ring(ring, dev_priv, i) {
 		acthd[i] = intel_ring_get_active_head(ring);
-		seqno[i] = ring->get_seqno(ring);
+		seqno[i] = intel_ring_get_seqno(ring);
 	}
 
 	intel_runtime_pm_put(dev_priv);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d099e960f9b8..37f4ef59fb4a 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2980,13 +2980,13 @@ i915_seqno_passed(uint32_t seq1, uint32_t seq2)
 
 static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
 {
-	return i915_seqno_passed(req->ring->get_seqno(req->ring),
+	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
 				 req->previous_seqno);
 }
 
 static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
 {
-	return i915_seqno_passed(req->ring->get_seqno(req->ring),
+	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
 				 req->seqno);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 01d0206ca4dd..3e137fc701cf 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -903,7 +903,7 @@ static void i915_record_ring_state(struct drm_device *dev,
 	ering->waiting = intel_engine_has_waiter(ring);
 	ering->instpm = I915_READ(RING_INSTPM(ring->mmio_base));
 	ering->acthd = intel_ring_get_active_head(ring);
-	ering->seqno = ring->get_seqno(ring);
+	ering->seqno = intel_ring_get_seqno(ring);
 	ering->start = I915_READ_START(ring);
 	ering->head = I915_READ_HEAD(ring);
 	ering->tail = I915_READ_TAIL(ring);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index da3c8aaa50a3..64502c0d2a81 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2875,7 +2875,7 @@ static int semaphore_passed(struct intel_engine_cs *ring)
 	if (signaller->hangcheck.deadlock >= I915_NUM_RINGS)
 		return -1;
 
-	if (i915_seqno_passed(signaller->get_seqno(signaller), seqno))
+	if (i915_seqno_passed(intel_ring_get_seqno(signaller), seqno))
 		return 1;
 
 	/* cursory check for an unkickable deadlock */
@@ -2979,7 +2979,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 		semaphore_clear_deadlocks(dev_priv);
 
 		acthd = intel_ring_get_active_head(ring);
-		seqno = ring->get_seqno(ring);
+		seqno = intel_ring_get_seqno(ring);
 
 		if (ring->hangcheck.seqno == seqno) {
 			if (ring_idle(ring, seqno)) {
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index cfb5f78a6e84..efca75bcace3 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -573,7 +573,7 @@ TRACE_EVENT(i915_gem_request_notify,
 	    TP_fast_assign(
 			   __entry->dev = ring->dev->primary->index;
 			   __entry->ring = ring->id;
-			   __entry->seqno = ring->get_seqno(ring);
+			   __entry->seqno = intel_ring_get_seqno(ring);
 			   ),
 
 	    TP_printk("dev=%u, ring=%u, seqno=%u",
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 740f10fa6331..69b966b4f71b 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -112,7 +112,7 @@ bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
 				 struct intel_breadcrumb *wait)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
-	u32 seqno = engine->get_seqno(engine);
+	u32 seqno = intel_ring_get_seqno(engine);
 	struct rb_node **p, *parent, *completed;
 	bool first;
 
@@ -222,7 +222,7 @@ void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
 			 * the overall latency in waking all the completed
 			 * clients.
 			 */
-			u32 seqno = engine->get_seqno(engine);
+			u32 seqno = intel_ring_get_seqno(engine);
 			while (i915_seqno_passed(seqno,
 						 to_crumb(next)->seqno)) {
 				struct rb_node *n = rb_next(next);
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 4e28f0b28f81..91e5ed6867e5 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1745,16 +1745,6 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
 	return 0;
 }
 
-static u32 gen8_get_seqno(struct intel_engine_cs *ring)
-{
-	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
-}
-
-static void gen8_set_seqno(struct intel_engine_cs *ring, u32 seqno)
-{
-	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);
-}
-
 static void bxt_seqno_barrier(struct intel_engine_cs *ring)
 {
 	/*
@@ -1770,14 +1760,6 @@ static void bxt_seqno_barrier(struct intel_engine_cs *ring)
 	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
-static void bxt_a_set_seqno(struct intel_engine_cs *ring, u32 seqno)
-{
-	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);
-
-	/* See bxt_a_get_seqno() explaining the reason for the clflush. */
-	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
-}
-
 static int gen8_emit_request(struct drm_i915_gem_request *request)
 {
 	struct intel_ringbuffer *ringbuf = request->ringbuf;
@@ -1802,7 +1784,7 @@ static int gen8_emit_request(struct drm_i915_gem_request *request)
 				(ring->status_page.gfx_addr +
 				(I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT)));
 	intel_logical_ring_emit(ringbuf, 0);
-	intel_logical_ring_emit(ringbuf, i915_gem_request_get_seqno(request));
+	intel_logical_ring_emit(ringbuf, request->seqno);
 	intel_logical_ring_emit(ringbuf, MI_USER_INTERRUPT);
 	intel_logical_ring_emit(ringbuf, MI_NOOP);
 	intel_logical_ring_advance_and_submit(request);
@@ -1972,12 +1954,8 @@ static int logical_render_ring_init(struct drm_device *dev)
 		ring->init_hw = gen8_init_render_ring;
 	ring->init_context = gen8_init_rcs_context;
 	ring->cleanup = intel_fini_pipe_control;
-	ring->get_seqno = gen8_get_seqno;
-	ring->set_seqno = gen8_set_seqno;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
+	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
 		ring->seqno_barrier = bxt_seqno_barrier;
-		ring->set_seqno = bxt_a_set_seqno;
-	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush_render;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2023,12 +2001,8 @@ static int logical_bsd_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS1_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	ring->get_seqno = gen8_get_seqno;
-	ring->set_seqno = gen8_set_seqno;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
+	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
 		ring->seqno_barrier = bxt_seqno_barrier;
-		ring->set_seqno = bxt_a_set_seqno;
-	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2052,8 +2026,6 @@ static int logical_bsd2_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS2_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	ring->get_seqno = gen8_get_seqno;
-	ring->set_seqno = gen8_set_seqno;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2077,12 +2049,8 @@ static int logical_blt_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_BCS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	ring->get_seqno = gen8_get_seqno;
-	ring->set_seqno = gen8_set_seqno;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
+	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
 		ring->seqno_barrier = bxt_seqno_barrier;
-		ring->set_seqno = bxt_a_set_seqno;
-	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2106,12 +2074,8 @@ static int logical_vebox_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VECS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	ring->get_seqno = gen8_get_seqno;
-	ring->set_seqno = gen8_set_seqno;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1)) {
+	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
 		ring->seqno_barrier = bxt_seqno_barrier;
-		ring->set_seqno = bxt_a_set_seqno;
-	}
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 3cd586eb24ba..14cd326ea99e 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1216,19 +1216,17 @@ static int gen8_rcs_signal(struct drm_i915_gem_request *signaller_req,
 		return ret;
 
 	for_each_ring(waiter, dev_priv, i) {
-		u32 seqno;
 		u64 gtt_offset = signaller->semaphore.signal_ggtt[i];
 		if (gtt_offset == MI_SEMAPHORE_SYNC_INVALID)
 			continue;
 
-		seqno = i915_gem_request_get_seqno(signaller_req);
 		intel_ring_emit(signaller, GFX_OP_PIPE_CONTROL(6));
 		intel_ring_emit(signaller, PIPE_CONTROL_GLOBAL_GTT_IVB |
 					   PIPE_CONTROL_QW_WRITE |
 					   PIPE_CONTROL_FLUSH_ENABLE);
 		intel_ring_emit(signaller, lower_32_bits(gtt_offset));
 		intel_ring_emit(signaller, upper_32_bits(gtt_offset));
-		intel_ring_emit(signaller, seqno);
+		intel_ring_emit(signaller, signaller_req->seqno);
 		intel_ring_emit(signaller, 0);
 		intel_ring_emit(signaller, MI_SEMAPHORE_SIGNAL |
 					   MI_SEMAPHORE_TARGET(waiter->id));
@@ -1257,18 +1255,16 @@ static int gen8_xcs_signal(struct drm_i915_gem_request *signaller_req,
 		return ret;
 
 	for_each_ring(waiter, dev_priv, i) {
-		u32 seqno;
 		u64 gtt_offset = signaller->semaphore.signal_ggtt[i];
 		if (gtt_offset == MI_SEMAPHORE_SYNC_INVALID)
 			continue;
 
-		seqno = i915_gem_request_get_seqno(signaller_req);
 		intel_ring_emit(signaller, (MI_FLUSH_DW + 1) |
 					   MI_FLUSH_DW_OP_STOREDW);
 		intel_ring_emit(signaller, lower_32_bits(gtt_offset) |
 					   MI_FLUSH_DW_USE_GTT);
 		intel_ring_emit(signaller, upper_32_bits(gtt_offset));
-		intel_ring_emit(signaller, seqno);
+		intel_ring_emit(signaller, signaller_req->seqno);
 		intel_ring_emit(signaller, MI_SEMAPHORE_SIGNAL |
 					   MI_SEMAPHORE_TARGET(waiter->id));
 		intel_ring_emit(signaller, 0);
@@ -1299,11 +1295,9 @@ static int gen6_signal(struct drm_i915_gem_request *signaller_req,
 		i915_reg_t mbox_reg = signaller->semaphore.mbox.signal[i];
 
 		if (i915_mmio_reg_valid(mbox_reg)) {
-			u32 seqno = i915_gem_request_get_seqno(signaller_req);
-
 			intel_ring_emit(signaller, MI_LOAD_REGISTER_IMM(1));
 			intel_ring_emit_reg(signaller, mbox_reg);
-			intel_ring_emit(signaller, seqno);
+			intel_ring_emit(signaller, signaller_req->seqno);
 		}
 	}
 
@@ -1338,7 +1332,7 @@ gen6_add_request(struct drm_i915_gem_request *req)
 
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
+	intel_ring_emit(ring, req->seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
 	__intel_ring_advance(ring);
 
@@ -1440,7 +1434,9 @@ static int
 pc_render_add_request(struct drm_i915_gem_request *req)
 {
 	struct intel_engine_cs *ring = req->ring;
-	u32 scratch_addr = ring->scratch.gtt_offset + 2 * CACHELINE_BYTES;
+	u32 addr = req->ring->status_page.gfx_addr +
+		(I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
+	u32 scratch_addr = addr;
 	int ret;
 
 	/* For Ironlake, MI_USER_INTERRUPT was deprecated and apparently
@@ -1455,11 +1451,12 @@ pc_render_add_request(struct drm_i915_gem_request *req)
 	if (ret)
 		return ret;
 
-	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) | PIPE_CONTROL_QW_WRITE |
-			PIPE_CONTROL_WRITE_FLUSH |
-			PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE);
-	intel_ring_emit(ring, ring->scratch.gtt_offset | PIPE_CONTROL_GLOBAL_GTT);
-	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
+	intel_ring_emit(ring,
+			GFX_OP_PIPE_CONTROL(4) |
+			PIPE_CONTROL_QW_WRITE |
+			PIPE_CONTROL_WRITE_FLUSH);
+	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
+	intel_ring_emit(ring, req->seqno);
 	intel_ring_emit(ring, 0);
 	PIPE_CONTROL_FLUSH(ring, scratch_addr);
 	scratch_addr += 2 * CACHELINE_BYTES; /* write to separate cachelines */
@@ -1473,12 +1470,12 @@ pc_render_add_request(struct drm_i915_gem_request *req)
 	scratch_addr += 2 * CACHELINE_BYTES;
 	PIPE_CONTROL_FLUSH(ring, scratch_addr);
 
-	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) | PIPE_CONTROL_QW_WRITE |
+	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) |
+			PIPE_CONTROL_QW_WRITE |
 			PIPE_CONTROL_WRITE_FLUSH |
-			PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE |
 			PIPE_CONTROL_NOTIFY);
-	intel_ring_emit(ring, ring->scratch.gtt_offset | PIPE_CONTROL_GLOBAL_GTT);
-	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
+	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
+	intel_ring_emit(ring, req->seqno);
 	intel_ring_emit(ring, 0);
 	__intel_ring_advance(ring);
 
@@ -1506,30 +1503,6 @@ gen6_seqno_barrier(struct intel_engine_cs *ring)
 	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
-static u32
-ring_get_seqno(struct intel_engine_cs *ring)
-{
-	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
-}
-
-static void
-ring_set_seqno(struct intel_engine_cs *ring, u32 seqno)
-{
-	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);
-}
-
-static u32
-pc_render_get_seqno(struct intel_engine_cs *ring)
-{
-	return ring->scratch.cpu_page[0];
-}
-
-static void
-pc_render_set_seqno(struct intel_engine_cs *ring, u32 seqno)
-{
-	ring->scratch.cpu_page[0] = seqno;
-}
-
 static bool
 gen5_ring_get_irq(struct intel_engine_cs *ring)
 {
@@ -1665,7 +1638,7 @@ i9xx_add_request(struct drm_i915_gem_request *req)
 
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
+	intel_ring_emit(ring, req->seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
 	__intel_ring_advance(ring);
 
@@ -2457,7 +2430,10 @@ void intel_ring_init_seqno(struct intel_engine_cs *ring, u32 seqno)
 			I915_WRITE(RING_SYNC_2(ring->mmio_base), 0);
 	}
 
-	ring->set_seqno(ring, seqno);
+	intel_write_status_page(ring, I915_GEM_HWS_INDEX, seqno);
+	if (ring->seqno_barrier)
+		ring->seqno_barrier(ring);
+
 	ring->hangcheck.seqno = seqno;
 }
 
@@ -2695,8 +2671,6 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->irq_put = gen8_ring_put_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
 		ring->seqno_barrier = gen6_seqno_barrier;
-		ring->get_seqno = ring_get_seqno;
-		ring->set_seqno = ring_set_seqno;
 		if (i915_semaphore_is_enabled(dev)) {
 			WARN_ON(!dev_priv->semaphore_obj);
 			ring->semaphore.sync_to = gen8_ring_sync;
@@ -2713,8 +2687,6 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->irq_put = gen6_ring_put_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
 		ring->seqno_barrier = gen6_seqno_barrier;
-		ring->get_seqno = ring_get_seqno;
-		ring->set_seqno = ring_set_seqno;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.sync_to = gen6_ring_sync;
 			ring->semaphore.signal = gen6_signal;
@@ -2739,8 +2711,6 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 	} else if (IS_GEN5(dev)) {
 		ring->add_request = pc_render_add_request;
 		ring->flush = gen4_render_ring_flush;
-		ring->get_seqno = pc_render_get_seqno;
-		ring->set_seqno = pc_render_set_seqno;
 		ring->irq_get = gen5_ring_get_irq;
 		ring->irq_put = gen5_ring_put_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT |
@@ -2751,8 +2721,6 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 			ring->flush = gen2_render_ring_flush;
 		else
 			ring->flush = gen4_render_ring_flush;
-		ring->get_seqno = ring_get_seqno;
-		ring->set_seqno = ring_set_seqno;
 		if (IS_GEN2(dev)) {
 			ring->irq_get = i8xx_ring_get_irq;
 			ring->irq_put = i8xx_ring_put_irq;
@@ -2828,8 +2796,6 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 		ring->flush = gen6_bsd_ring_flush;
 		ring->add_request = gen6_add_request;
 		ring->seqno_barrier = gen6_seqno_barrier;
-		ring->get_seqno = ring_get_seqno;
-		ring->set_seqno = ring_set_seqno;
 		if (INTEL_INFO(dev)->gen >= 8) {
 			ring->irq_enable_mask =
 				GT_RENDER_USER_INTERRUPT << GEN8_VCS1_IRQ_SHIFT;
@@ -2867,8 +2833,6 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 		ring->mmio_base = BSD_RING_BASE;
 		ring->flush = bsd_ring_flush;
 		ring->add_request = i9xx_add_request;
-		ring->get_seqno = ring_get_seqno;
-		ring->set_seqno = ring_set_seqno;
 		if (IS_GEN5(dev)) {
 			ring->irq_enable_mask = ILK_BSD_USER_INTERRUPT;
 			ring->irq_get = gen5_ring_get_irq;
@@ -2901,8 +2865,6 @@ int intel_init_bsd2_ring_buffer(struct drm_device *dev)
 	ring->flush = gen6_bsd_ring_flush;
 	ring->add_request = gen6_add_request;
 	ring->seqno_barrier = gen6_seqno_barrier;
-	ring->get_seqno = ring_get_seqno;
-	ring->set_seqno = ring_set_seqno;
 	ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_VCS2_IRQ_SHIFT;
 	ring->irq_get = gen8_ring_get_irq;
@@ -2932,8 +2894,6 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
 	ring->flush = gen6_ring_flush;
 	ring->add_request = gen6_add_request;
 	ring->seqno_barrier = gen6_seqno_barrier;
-	ring->get_seqno = ring_get_seqno;
-	ring->set_seqno = ring_set_seqno;
 	if (INTEL_INFO(dev)->gen >= 8) {
 		ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_BCS_IRQ_SHIFT;
@@ -2990,8 +2950,6 @@ int intel_init_vebox_ring_buffer(struct drm_device *dev)
 	ring->flush = gen6_ring_flush;
 	ring->add_request = gen6_add_request;
 	ring->seqno_barrier = gen6_seqno_barrier;
-	ring->get_seqno = ring_get_seqno;
-	ring->set_seqno = ring_set_seqno;
 
 	if (INTEL_INFO(dev)->gen >= 8) {
 		ring->irq_enable_mask =
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 2c2454ccdd96..7ad06cbef6be 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -219,9 +219,6 @@ struct  intel_engine_cs {
 	 * monotonic, even if not coherent.
 	 */
 	void		(*seqno_barrier)(struct intel_engine_cs *ring);
-	u32		(*get_seqno)(struct intel_engine_cs *ring);
-	void		(*set_seqno)(struct intel_engine_cs *ring,
-				     u32 seqno);
 	int		(*dispatch_execbuffer)(struct drm_i915_gem_request *req,
 					       u64 offset, u32 length,
 					       unsigned dispatch_flags);
@@ -501,6 +498,10 @@ int intel_init_blt_ring_buffer(struct drm_device *dev);
 int intel_init_vebox_ring_buffer(struct drm_device *dev);
 
 u64 intel_ring_get_active_head(struct intel_engine_cs *ring);
+static inline u32 intel_ring_get_seqno(struct intel_engine_cs *ring)
+{
+	return intel_read_status_page(ring, I915_GEM_HWS_INDEX);
+}
 
 int init_workarounds_ring(struct intel_engine_cs *ring);
 
-- 
2.6.3

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Re: [PATCH 18/32] drm/i915: Use HWS for seqno tracking everywhere

[Dave Gordon]

On 11/12/15 11:33, Chris Wilson wrote:
> By using the same address for storing the HWS on every platform, we can
> remove the platform specific vfuncs and reduce the get-seqno routine to
> a single read of a cached memory location.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c      | 10 ++--
>   drivers/gpu/drm/i915/i915_drv.h          |  4 +-
>   drivers/gpu/drm/i915/i915_gpu_error.c    |  2 +-
>   drivers/gpu/drm/i915/i915_irq.c          |  4 +-
>   drivers/gpu/drm/i915/i915_trace.h        |  2 +-
>   drivers/gpu/drm/i915/intel_breadcrumbs.c |  4 +-
>   drivers/gpu/drm/i915/intel_lrc.c         | 46 ++---------------
>   drivers/gpu/drm/i915/intel_ringbuffer.c  | 86 ++++++++------------------------
>   drivers/gpu/drm/i915/intel_ringbuffer.h  |  7 +--
>   9 files changed, 43 insertions(+), 122 deletions(-)

This looks worthwhile, and most of it is obviously correct, just being a 
simple transformation. But it looks like pc_render_add_request() 
actually changes functionality somewhat:

> @@ -1440,7 +1434,9 @@ static int
>   pc_render_add_request(struct drm_i915_gem_request *req)
>   {
>   	struct intel_engine_cs *ring = req->ring;
> -	u32 scratch_addr = ring->scratch.gtt_offset + 2 * CACHELINE_BYTES;
> +	u32 addr = req->ring->status_page.gfx_addr +
> +		(I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
> +	u32 scratch_addr = addr;
>   	int ret;
>
>   	/* For Ironlake, MI_USER_INTERRUPT was deprecated and apparently
> @@ -1455,11 +1451,12 @@ pc_render_add_request(struct drm_i915_gem_request *req)
>   	if (ret)
>   		return ret;
>
> -	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) | PIPE_CONTROL_QW_WRITE |
> -			PIPE_CONTROL_WRITE_FLUSH |
> -			PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE);
> -	intel_ring_emit(ring, ring->scratch.gtt_offset | PIPE_CONTROL_GLOBAL_GTT);
> -	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
> +	intel_ring_emit(ring,
> +			GFX_OP_PIPE_CONTROL(4) |
> +			PIPE_CONTROL_QW_WRITE |
> +			PIPE_CONTROL_WRITE_FLUSH);
> +	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
> +	intel_ring_emit(ring, req->seqno);
>   	intel_ring_emit(ring, 0);
>   	PIPE_CONTROL_FLUSH(ring, scratch_addr);
>   	scratch_addr += 2 * CACHELINE_BYTES; /* write to separate cachelines */
> @@ -1473,12 +1470,12 @@ pc_render_add_request(struct drm_i915_gem_request *req)
>   	scratch_addr += 2 * CACHELINE_BYTES;
>   	PIPE_CONTROL_FLUSH(ring, scratch_addr);
>
> -	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) | PIPE_CONTROL_QW_WRITE |
> +	intel_ring_emit(ring, GFX_OP_PIPE_CONTROL(4) |
> +			PIPE_CONTROL_QW_WRITE |
>   			PIPE_CONTROL_WRITE_FLUSH |
> -			PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE |
>   			PIPE_CONTROL_NOTIFY);
> -	intel_ring_emit(ring, ring->scratch.gtt_offset | PIPE_CONTROL_GLOBAL_GTT);
> -	intel_ring_emit(ring, i915_gem_request_get_seqno(req));
> +	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
> +	intel_ring_emit(ring, req->seqno);
>   	intel_ring_emit(ring, 0);
>   	__intel_ring_advance(ring);

So previously, we wrote the seqno and other dummy data into the SCRATCH 
page, whereas now it's going to the HWSP. Does that make the scratch 
page redundant? Or are there other bits of code that write other stuff 
into it?

Then, the new code not only writes in dword I915_GEM_HWS_INDEX of the 
HWSP, but also at multiple cache lines above this address. Do those 
write have to be to the same page as the seqno, or could they still go 
to the scratch page?

If the latter, I think we'd need to flag this in a big comment above the 
definition of I915_GEM_HWS_INDEX, because it's not just defining a 
single word as it appears, but rather a large block that will be 
scribbled on.

(Note: TDR and the preemption code each require some extra locations in 
the HWSP; they mustn't be scribbled over with dummy data).

Finally, we seem to have lost the PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE 
bits; was that deliberate? And should it have been in a separate patch?

.Dave.
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Re: [PATCH 18/32] drm/i915: Use HWS for seqno tracking everywhere

[Chris Wilson]

On Mon, Jan 04, 2016 at 06:11:56PM +0000, Dave Gordon wrote:
> So previously, we wrote the seqno and other dummy data into the
> SCRATCH page, whereas now it's going to the HWSP. Does that make the
> scratch page redundant? Or are there other bits of code that write
> other stuff into it?

The scratch page is used on gen6+ for workaround flushes, and gen8+ for
per-bb workarounds.

> Then, the new code not only writes in dword I915_GEM_HWS_INDEX of
> the HWSP, but also at multiple cache lines above this address. Do
> those write have to be to the same page as the seqno, or could they
> still go to the scratch page?

The writes only exist to act as a flush of the pipecontrols themselves,
what they write and where is irrelevant. Afaik, writing to separate
cachelines is paranoia, but does not complicate the code too much.
 
> If the latter, I think we'd need to flag this in a big comment above
> the definition of I915_GEM_HWS_INDEX, because it's not just defining
> a single word as it appears, but rather a large block that will be
> scribbled on.
>
> (Note: TDR and the preemption code each require some extra locations
> in the HWSP; they mustn't be scribbled over with dummy data).

Sure. But on gen5 only the first 20 dwords are reserved for use by the
hw, the rest of the page is our to use. And since the removal of DRI1,
there is no other use.
 
> Finally, we seem to have lost the
> PIPE_CONTROL_TEXTURE_CACHE_INVALIDATE bits; was that deliberate? And
> should it have been in a separate patch?

It is the wrong flag. Separate patch would be that we don't need the
pipecontrols anyway, which was sent last year.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[PATCH 19/32] drm/i915: Check the CPU cached value of seqno after waking the waiter

[Chris Wilson]

If we have multiple waiters, we may find that many complete on the same
wake up. If we first inspect the seqno from the CPU cache, we may reduce
the number of heavyweight coherent seqno reads we require.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index f3c1e268f614..15495b8112f9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1288,6 +1288,12 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 
 wakeup:		set_task_state(wait.task, state);
 
+		/* Before we do the heavier coherent read of the seqno,
+		 * check the value (hopefully) in the CPU cacheline.
+		 */
+		if (i915_gem_request_completed(req))
+			break;
+
 		/* Ensure our read of the seqno is coherent so that we
 		 * do not "miss an interrupt" (i.e. if this is the last
 		 * request and the seqno write from the GPU is not visible
@@ -1299,11 +1305,11 @@ wakeup:		set_task_state(wait.task, state);
 		 * but it is easier and safer to do it every time the waiter
 		 * is woken.
 		 */
-		if (req->ring->seqno_barrier)
+		if (req->ring->seqno_barrier) {
 			req->ring->seqno_barrier(req->ring);
-
-		if (i915_gem_request_completed(req))
-			break;
+			if (i915_gem_request_completed(req))
+				break;
+		}
 
 		/* We need to check whether any gpu reset happened in between
 		 * the request being submitted and now. If a reset has occurred,
-- 
2.6.3

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[PATCH 20/32] drm/i915: Replace manual barrier() with READ_ONCE() in HWS accessor

[Chris Wilson]

When reading from the HWS page, we use barrier() to prevent the compiler
optimising away the read from the volatile (may be updated by the GPU)
memory address. This is more suited to READ_ONCE(); make it so.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/intel_ringbuffer.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 7ad06cbef6be..a35c17106f4b 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -416,8 +416,7 @@ intel_read_status_page(struct intel_engine_cs *ring,
 		       int reg)
 {
 	/* Ensure that the compiler doesn't optimize away the load. */
-	barrier();
-	return ring->status_page.page_addr[reg];
+	return READ_ONCE(ring->status_page.page_addr[reg]);
 }
 
 static inline void
-- 
2.6.3

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[PATCH 21/32] drm/i915: Broadwell execlists needs exactly the same seqno w/a as legacy

[Chris Wilson]

In legacy mode, we use the gen6 seqno barrier to insert a delay after
the interrupt before reading the seqno (as the seqno write is not
flushed before the interrupt is sent, the interrupt arrives before the
seqno is visible). Execlists ignored the evidence of igt.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_lrc.c | 39 +++++++++++++++++++++------------------
 1 file changed, 21 insertions(+), 18 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 91e5ed6867e5..a73c5e671423 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1745,18 +1745,24 @@ static int gen8_emit_flush_render(struct drm_i915_gem_request *request,
 	return 0;
 }
 
-static void bxt_seqno_barrier(struct intel_engine_cs *ring)
+static void
+gen6_seqno_barrier(struct intel_engine_cs *ring)
 {
-	/*
-	 * On BXT A steppings there is a HW coherency issue whereby the
-	 * MI_STORE_DATA_IMM storing the completed request's seqno
-	 * occasionally doesn't invalidate the CPU cache. Work around this by
-	 * clflushing the corresponding cacheline whenever the caller wants
-	 * the coherency to be guaranteed. Note that this cacheline is known
-	 * to be clean at this point, since we only write it in
-	 * bxt_a_set_seqno(), where we also do a clflush after the write. So
-	 * this clflush in practice becomes an invalidate operation.
+	/* Workaround to force correct ordering between irq and seqno writes on
+	 * ivb (and maybe also on snb) by reading from a CS register (like
+	 * ACTHD) before reading the status page.
+	 *
+	 * Note that this effectively effectively stalls the read by the time
+	 * it takes to do a memory transaction, which more or less ensures
+	 * that the write from the GPU has sufficient time to invalidate
+	 * the CPU cacheline. Alternatively we could delay the interrupt from
+	 * the CS ring to give the write time to land, but that would incur
+	 * a delay after every batch i.e. much more frequent than a delay
+	 * when waiting for the interrupt (with the same net latency).
 	 */
+	struct drm_i915_private *dev_priv = ring->i915;
+	POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
+
 	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
@@ -1954,8 +1960,7 @@ static int logical_render_ring_init(struct drm_device *dev)
 		ring->init_hw = gen8_init_render_ring;
 	ring->init_context = gen8_init_rcs_context;
 	ring->cleanup = intel_fini_pipe_control;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
-		ring->seqno_barrier = bxt_seqno_barrier;
+	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush_render;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2001,8 +2006,7 @@ static int logical_bsd_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS1_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
-		ring->seqno_barrier = bxt_seqno_barrier;
+	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2026,6 +2030,7 @@ static int logical_bsd2_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VCS2_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
+	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2049,8 +2054,7 @@ static int logical_blt_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_BCS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
-		ring->seqno_barrier = bxt_seqno_barrier;
+	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
@@ -2074,8 +2078,7 @@ static int logical_vebox_ring_init(struct drm_device *dev)
 		GT_CONTEXT_SWITCH_INTERRUPT << GEN8_VECS_IRQ_SHIFT;
 
 	ring->init_hw = gen8_init_common_ring;
-	if (IS_BXT_REVID(dev, 0, BXT_REVID_A1))
-		ring->seqno_barrier = bxt_seqno_barrier;
+	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
 	ring->irq_get = gen8_logical_ring_get_irq;
-- 
2.6.3

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Re: [PATCH 21/32] drm/i915: Broadwell execlists needs exactly the same seqno w/a as legacy

[Jesse Barnes]

On 12/11/2015 03:33 AM, Chris Wilson wrote:
> +	 * Note that this effectively effectively stalls the read by the time
> +	 * it takes to do a memory transaction, which more or less ensures
> +	 * that the write from the GPU has sufficient time to invalidate
> +	 * the CPU cacheline. Alternatively we could delay the interrupt from
> +	 * the CS ring to give the write time to land, but that would incur
> +	 * a delay after every batch i.e. much more frequent than a delay
> +	 * when waiting for the interrupt (with the same net latency).
>  	 */
> +	struct drm_i915_private *dev_priv = ring->i915;
> +	POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
> +
>  	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);

Funnily enough, the interrupt ought to provide the same behavior as the MMIO read, i.e. flush outstanding system memory writes ahead of it.  The fact that we need it *plus* a CPU cache flush definitely means we're still missing something...

But hey, whatever works is good for now...

Jesse
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Re: [PATCH 21/32] drm/i915: Broadwell execlists needs exactly the same seqno w/a as legacy

[Chris Wilson]

On Mon, Jan 04, 2016 at 01:34:46PM -0800, Jesse Barnes wrote:
> On 12/11/2015 03:33 AM, Chris Wilson wrote:
> > +	 * Note that this effectively effectively stalls the read by the time
> > +	 * it takes to do a memory transaction, which more or less ensures
> > +	 * that the write from the GPU has sufficient time to invalidate
> > +	 * the CPU cacheline. Alternatively we could delay the interrupt from
> > +	 * the CS ring to give the write time to land, but that would incur
> > +	 * a delay after every batch i.e. much more frequent than a delay
> > +	 * when waiting for the interrupt (with the same net latency).
> >  	 */
> > +	struct drm_i915_private *dev_priv = ring->i915;
> > +	POSTING_READ_FW(RING_ACTHD(ring->mmio_base));
> > +
> >  	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
> 
> Funnily enough, the interrupt ought to provide the same behavior as the MMIO read, i.e. flush outstanding system memory writes ahead of it.  The fact that we need it *plus* a CPU cache flush definitely means we're still missing something...

It is purely a timing issue (aside from bxt-a requiring the w/a). A
udelay() works just as well, but the question is what value to wait for,
which is where the above empiricism kicks in. (Another example would be
adding 32 dword writes into the ring between the seqno and
MI_USER_INTERRUPT).
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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[PATCH 22/32] drm/i915: Stop setting wraparound seqno on initialisation

[Chris Wilson]

We have testcases to ensure that seqno wraparound works fine, so we can
forgo forcing everyone to encounter seqno wraparound during early
uptime. seqno wraparound incurs a full GPU stall so not forcing it
will eliminate one jitter from the early system. Using the testcases, we
have very deterministic testing which given how difficult it would be to
debug an issue (GPU hang) stemming from a wraparound using pure
postmortem analysis I see no value in forcing a wrap during boot.

Advancing the global next_seqno after a GPU reset is equally pointless.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 16 +---------------
 1 file changed, 1 insertion(+), 15 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 15495b8112f9..d595d72e53b1 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -4831,14 +4831,6 @@ i915_gem_init_hw(struct drm_device *dev)
 		}
 	}
 
-	/*
-	 * Increment the next seqno by 0x100 so we have a visible break
-	 * on re-initialisation
-	 */
-	ret = i915_gem_set_seqno(dev, dev_priv->next_seqno+0x100);
-	if (ret)
-		goto out;
-
 	/* Now it is safe to go back round and do everything else: */
 	for_each_ring(ring, dev_priv, i) {
 		struct drm_i915_gem_request *req;
@@ -5018,13 +5010,7 @@ i915_gem_load(struct drm_device *dev)
 		dev_priv->num_fence_regs =
 				I915_READ(vgtif_reg(avail_rs.fence_num));
 
-	/*
-	 * Set initial sequence number for requests.
-	 * Using this number allows the wraparound to happen early,
-	 * catching any obvious problems.
-	 */
-	dev_priv->next_seqno = ((u32)~0 - 0x1100);
-	dev_priv->last_seqno = ((u32)~0 - 0x1101);
+	dev_priv->next_seqno = 1;
 
 	/* Initialize fence registers to zero */
 	INIT_LIST_HEAD(&dev_priv->mm.fence_list);
-- 
2.6.3

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[PATCH 23/32] drm/i915: Only query timestamp when measuring elapsed time

[Chris Wilson]

Avoid the two calls to ktime_get_raw_ns() (at best it reads the TSC) as
we only need to compute the elapsed time for a timed wait.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d595d72e53b1..ca327c0e73f1 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1222,7 +1222,6 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
 	struct intel_breadcrumb wait;
 	unsigned long timeout_remain;
-	s64 before, now;
 	int ret = 0;
 
 	might_sleep();
@@ -1241,13 +1240,12 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 		if (*timeout == 0)
 			return -ETIME;
 
+		/* Record current time in case interrupted, or wedged */
 		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
+		*timeout += ktime_get_raw_ns();
 	}
 
-	/* Record current time in case interrupted by signal, or wedged */
 	trace_i915_gem_request_wait_begin(req);
-	before = ktime_get_raw_ns();
-
 	if (INTEL_INFO(req->i915)->gen >= 6)
 		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
@@ -1324,13 +1322,12 @@ wakeup:		set_task_state(wait.task, state);
 out:
 	intel_engine_remove_breadcrumb(req->ring, &wait);
 	__set_task_state(wait.task, TASK_RUNNING);
-	now = ktime_get_raw_ns();
 	trace_i915_gem_request_wait_end(req);
 
 	if (timeout) {
-		s64 tres = *timeout - (now - before);
-
-		*timeout = tres < 0 ? 0 : tres;
+		*timeout -= ktime_get_raw_ns();
+		if (*timeout < 0)
+			*timeout = 0;
 
 		/*
 		 * Apparently ktime isn't accurate enough and occasionally has a
-- 
2.6.3

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[PATCH 24/32] drm/i915: On GPU reset, set the HWS breadcrumb to the last seqno

[Chris Wilson]

After the GPU reset and we discard all of the incomplete requests, mark
the GPU as having advanced to the last_submitted_seqno (as having
completed the requests and ready for fresh work). The impact of this is
negligble, as all the requests will be considered completed by this
point, it just brings the HWS into line with expectations for external
viewers.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index ca327c0e73f1..78bcd231b100 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2836,6 +2836,8 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
 		buffer->last_retired_head = buffer->tail;
 		intel_ring_update_space(buffer);
 	}
+
+	intel_ring_init_seqno(ring, ring->last_submitted_seqno);
 }
 
 void i915_gem_reset(struct drm_device *dev)
-- 
2.6.3

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[PATCH 25/32] drm/i915: Convert trace-irq to the breadcrumb waiter

[Chris Wilson]

If we convert the tracing over from direct use of ring->irq_get() and
over to the breadcrumb infrastructure, we only have a single user of the
ring->irq_get and so we will be able to simplify the driver routines
(eliminating the redundant validation and irq refcounting).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h          |  8 -------
 drivers/gpu/drm/i915/i915_gem.c          |  6 -----
 drivers/gpu/drm/i915/i915_trace.h        |  2 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 39 ++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.h  |  4 +++-
 5 files changed, 43 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 37f4ef59fb4a..dabfb043362f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3625,12 +3625,4 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 			    schedule_timeout_uninterruptible(remaining_jiffies);
 	}
 }
-
-static inline void i915_trace_irq_get(struct intel_engine_cs *ring,
-				      struct drm_i915_gem_request *req)
-{
-	if (ring->trace_irq_req == NULL && ring->irq_get(ring))
-		i915_gem_request_assign(&ring->trace_irq_req, req);
-}
-
 #endif
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 78bcd231b100..fdd9dd5296e9 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2907,12 +2907,6 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 		i915_gem_object_retire__read(obj, ring->id);
 	}
 
-	if (unlikely(ring->trace_irq_req &&
-		     i915_gem_request_completed(ring->trace_irq_req))) {
-		ring->irq_put(ring);
-		i915_gem_request_assign(&ring->trace_irq_req, NULL);
-	}
-
 	WARN_ON(i915_verify_lists(ring->dev));
 }
 
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index efca75bcace3..628008e6c24f 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -503,7 +503,7 @@ TRACE_EVENT(i915_gem_ring_dispatch,
 			   __entry->ring = ring->id;
 			   __entry->seqno = i915_gem_request_get_seqno(req);
 			   __entry->flags = flags;
-			   i915_trace_irq_get(ring, req);
+			   intel_breadcrumbs_enable_trace(req);
 			   ),
 
 	    TP_printk("dev=%u, ring=%u, seqno=%u, flags=%x",
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 69b966b4f71b..ea5ee3f7fe01 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -258,17 +258,56 @@ void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
 	spin_unlock(&b->lock);
 }
 
+static void intel_breadcrumbs_tracer(struct work_struct *work)
+{
+	struct intel_breadcrumbs *b =
+		container_of(work, struct intel_breadcrumbs, trace);
+	struct intel_rps_client rps;
+
+	INIT_LIST_HEAD(&rps.link);
+
+	do {
+		struct drm_i915_gem_request *request;
+
+		spin_lock(&b->lock);
+		request = b->trace_request;
+		b->trace_request = NULL;
+		spin_unlock(&b->lock);
+		if (request == NULL)
+			return;
+
+		__i915_wait_request(request, true, NULL, &rps);
+		i915_gem_request_unreference__unlocked(request);
+	} while (1);
+}
+
+void intel_breadcrumbs_enable_trace(struct drm_i915_gem_request *request)
+{
+	struct intel_breadcrumbs *b = &request->ring->breadcrumbs;
+
+	spin_lock(&b->lock);
+	if (b->trace_request == NULL) {
+		b->trace_request = i915_gem_request_reference(request);
+		queue_work(system_long_wq, &b->trace);
+	}
+	spin_unlock(&b->lock);
+}
+
 void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
 	spin_lock_init(&b->lock);
 	setup_timer(&b->fake_irq, intel_breadcrumbs_fake_irq, (unsigned long)b);
+	INIT_WORK(&b->trace, intel_breadcrumbs_tracer);
 }
 
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
+	cancel_work_sync(&b->trace);
+	i915_gem_request_unreference(b->trace_request);
+
 	del_timer_sync(&b->fake_irq);
 }
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index a35c17106f4b..0fd6395f1a1b 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -182,6 +182,8 @@ struct  intel_engine_cs {
 		struct rb_root requests; /* sorted by retirement */
 		struct task_struct *first_waiter; /* bh for user interrupts */
 		struct timer_list fake_irq; /* used after a missed interrupt */
+		struct work_struct trace;
+		struct drm_i915_gem_request *trace_request;
 		bool irq_enabled;
 		bool rpm_wakelock;
 	} breadcrumbs;
@@ -198,7 +200,6 @@ struct  intel_engine_cs {
 
 	unsigned irq_refcount; /* protected by dev_priv->irq_lock */
 	u32		irq_enable_mask;	/* bitmask to enable ring interrupt */
-	struct drm_i915_gem_request *trace_irq_req;
 	bool __must_check (*irq_get)(struct intel_engine_cs *ring);
 	void		(*irq_put)(struct intel_engine_cs *ring);
 
@@ -555,6 +556,7 @@ bool intel_engine_add_breadcrumb(struct intel_engine_cs *engine,
 				 struct intel_breadcrumb *wait);
 void intel_engine_remove_breadcrumb(struct intel_engine_cs *engine,
 				    struct intel_breadcrumb *wait);
+void intel_breadcrumbs_enable_trace(struct drm_i915_gem_request *request);
 static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
 {
 	return READ_ONCE(engine->breadcrumbs.first_waiter);
-- 
2.6.3

_______________________________________________
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Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH v2] drm/i915: Convert trace-irq to the breadcrumb waiter

[Chris Wilson]

If we convert the tracing over from direct use of ring->irq_get() and
over to the breadcrumb infrastructure, we only have a single user of the
ring->irq_get and so we will be able to simplify the driver routines
(eliminating the redundant validation and irq refcounting).

v2: Move to a signalling framework based upon the waiter.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_drv.h          |   8 --
 drivers/gpu/drm/i915/i915_gem.c          |   6 --
 drivers/gpu/drm/i915/i915_trace.h        |   2 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c | 132 +++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/intel_ringbuffer.h  |   6 +-
 5 files changed, 138 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 37f4ef59fb4a..dabfb043362f 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3625,12 +3625,4 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms)
 			    schedule_timeout_uninterruptible(remaining_jiffies);
 	}
 }
-
-static inline void i915_trace_irq_get(struct intel_engine_cs *ring,
-				      struct drm_i915_gem_request *req)
-{
-	if (ring->trace_irq_req == NULL && ring->irq_get(ring))
-		i915_gem_request_assign(&ring->trace_irq_req, req);
-}
-
 #endif
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 1ef677f3aac8..550ccd7873ab 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2907,12 +2907,6 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 		i915_gem_object_retire__read(obj, ring->id);
 	}
 
-	if (unlikely(ring->trace_irq_req &&
-		     i915_gem_request_completed(ring->trace_irq_req))) {
-		ring->irq_put(ring);
-		i915_gem_request_assign(&ring->trace_irq_req, NULL);
-	}
-
 	WARN_ON(i915_verify_lists(ring->dev));
 }
 
diff --git a/drivers/gpu/drm/i915/i915_trace.h b/drivers/gpu/drm/i915/i915_trace.h
index efca75bcace3..3446abb4cf59 100644
--- a/drivers/gpu/drm/i915/i915_trace.h
+++ b/drivers/gpu/drm/i915/i915_trace.h
@@ -503,7 +503,7 @@ TRACE_EVENT(i915_gem_ring_dispatch,
 			   __entry->ring = ring->id;
 			   __entry->seqno = i915_gem_request_get_seqno(req);
 			   __entry->flags = flags;
-			   i915_trace_irq_get(ring, req);
+			   intel_engine_add_signal(req);
 			   ),
 
 	    TP_printk("dev=%u, ring=%u, seqno=%u, flags=%x",
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index aefea0bf8a32..faf082b43202 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -22,6 +22,8 @@
  *
  */
 
+#include <linux/kthread.h>
+
 #include "i915_drv.h"
 
 static void intel_breadcrumbs_fake_irq(unsigned long data)
@@ -266,9 +268,139 @@ void intel_engine_init_breadcrumbs(struct intel_engine_cs *engine)
 	setup_timer(&b->fake_irq, intel_breadcrumbs_fake_irq, (unsigned long)b);
 }
 
+struct signal {
+	struct rb_node node;
+	struct intel_wait wait;
+	struct drm_i915_gem_request *request;
+};
+
+static bool signal_complete(struct signal *signal)
+{
+	struct drm_i915_gem_request *rq = signal->request;
+
+	if (signal == NULL)
+		return false;
+
+	if (intel_wait_complete(&signal->wait))
+		return true;
+
+	if (i915_gem_request_completed(rq))
+		return true;
+
+	if (rq->ring->seqno_barrier) {
+		rq->ring->seqno_barrier(rq->ring);
+		if (i915_gem_request_completed(rq))
+			return true;
+	}
+
+	if (rq->reset_counter != i915_reset_counter(&rq->i915->gpu_error))
+		return true;
+
+	return false;
+}
+
+static struct signal *to_signal(struct rb_node *rb)
+{
+	return container_of(rb, struct signal, node);
+}
+
+static int intel_breadcrumbs_signaller(void *arg)
+{
+	struct intel_engine_cs *engine = arg;
+
+	do {
+		struct signal *signal;
+
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		spin_lock(&engine->breadcrumbs.lock);
+		signal = to_signal(rb_first(&engine->breadcrumbs.signals));
+		spin_unlock(&engine->breadcrumbs.lock);
+
+		if (signal_complete(signal)) {
+			intel_engine_remove_wait(engine, &signal->wait);
+
+			i915_gem_request_unreference__unlocked(signal->request);
+
+			spin_lock(&engine->breadcrumbs.lock);
+			rb_erase(&signal->node, &engine->breadcrumbs.signals);
+			spin_unlock(&engine->breadcrumbs.lock);
+
+			kfree(signal);
+		} else {
+			i915_queue_hangcheck(engine->i915);
+
+			if (kthread_should_stop())
+				break;
+
+			schedule();
+		}
+	} while (1);
+
+	return 0;
+}
+
+int intel_engine_add_signal(struct drm_i915_gem_request *request)
+{
+	struct intel_engine_cs *engine = request->ring;
+	struct intel_breadcrumbs *b = &engine->breadcrumbs;
+	struct rb_node *parent, **p;
+	struct task_struct *task;
+	struct signal *signal;
+
+	signal = kmalloc(sizeof(*signal), GFP_ATOMIC);
+	if (signal == NULL)
+		return -ENOMEM;
+
+	task = READ_ONCE(b->signaller);
+	if (task == NULL) {
+		spin_lock(&b->lock);
+		task = kthread_create(intel_breadcrumbs_signaller,
+				      engine, "irq/i915-%d", engine->id);
+		if (!IS_ERR(task))
+			b->signaller = task;
+		spin_unlock(&b->lock);
+
+		if (IS_ERR(task)) {
+			kfree(signal);
+			return PTR_ERR(task);
+		}
+	}
+
+	signal->wait.task = task;
+	signal->wait.seqno = request->seqno;
+
+	signal->request = i915_gem_request_reference(request);
+
+	spin_lock(&b->lock);
+	parent = NULL;
+	p = &b->signals.rb_node;
+	while (*p) {
+		parent = *p;
+		if (i915_seqno_passed(signal->wait.seqno,
+				      to_signal(parent)->wait.seqno))
+			p = &parent->rb_right;
+		else
+			p = &parent->rb_left;
+	}
+	rb_link_node(&signal->node, parent, p);
+	rb_insert_color(&signal->node, &b->signals);
+	spin_unlock(&b->lock);
+
+	if (intel_engine_add_wait(engine, &signal->wait)) {
+		intel_engine_enable_irq(engine);
+		wake_up_process(task);
+	}
+
+	return 0;
+}
+
 void intel_engine_fini_breadcrumbs(struct intel_engine_cs *engine)
 {
 	struct intel_breadcrumbs *b = &engine->breadcrumbs;
 
+	if (b->signaller)
+		kthread_stop(b->signaller);
+
 	del_timer_sync(&b->fake_irq);
 }
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 3c390ce26919..cff3f15f9859 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -144,6 +144,8 @@ struct  i915_ctx_workarounds {
 	struct drm_i915_gem_object *obj;
 };
 
+struct drm_i915_gem_request;
+
 struct  intel_engine_cs {
 	const char	*name;
 	enum intel_ring_id {
@@ -180,7 +182,9 @@ struct  intel_engine_cs {
 	struct intel_breadcrumbs {
 		spinlock_t lock; /* protects the lists of requests */
 		struct rb_root waiters; /* sorted by retirement */
+		struct rb_root signals; /* sorted by retirement */
 		struct task_struct *first_waiter; /* bh for user interrupts */
+		struct task_struct *signaller; /* used for fence signalling */
 		struct timer_list fake_irq; /* used after a missed interrupt */
 		bool irq_enabled;
 		bool rpm_wakelock;
@@ -198,7 +202,6 @@ struct  intel_engine_cs {
 
 	unsigned irq_refcount; /* protected by dev_priv->irq_lock */
 	u32		irq_enable_mask;	/* bitmask to enable ring interrupt */
-	struct drm_i915_gem_request *trace_irq_req;
 	bool __must_check (*irq_get)(struct intel_engine_cs *ring);
 	void		(*irq_put)(struct intel_engine_cs *ring);
 
@@ -554,6 +557,7 @@ bool intel_engine_add_wait(struct intel_engine_cs *engine,
 			   struct intel_wait *wait);
 void intel_engine_remove_wait(struct intel_engine_cs *engine,
 			      struct intel_wait *wait);
+int intel_engine_add_signal(struct drm_i915_gem_request *request);
 static inline bool intel_engine_has_waiter(struct intel_engine_cs *engine)
 {
 	return READ_ONCE(engine->breadcrumbs.first_waiter);
-- 
2.6.3

_______________________________________________
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Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 1/3] drm/i915: Move GEM request routines to i915_gem_request.c

[Chris Wilson]

Migrate the request operations out of the main body of i915_gem.c and
into their own C file for easier expansion.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/Makefile           |   1 +
 drivers/gpu/drm/i915/i915_drv.h         | 186 +-----------
 drivers/gpu/drm/i915/i915_gem.c         | 502 +------------------------------
 drivers/gpu/drm/i915/i915_gem_request.c | 513 ++++++++++++++++++++++++++++++++
 drivers/gpu/drm/i915/i915_gem_request.h | 209 +++++++++++++
 5 files changed, 732 insertions(+), 679 deletions(-)
 create mode 100644 drivers/gpu/drm/i915/i915_gem_request.c
 create mode 100644 drivers/gpu/drm/i915/i915_gem_request.h

diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index d3b9d3618719..3df88be4752e 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -29,6 +29,7 @@ i915-y += i915_cmd_parser.o \
 	  i915_gem_gtt.o \
 	  i915_gem.o \
 	  i915_gem_render_state.o \
+	  i915_gem_request.o \
 	  i915_gem_shrinker.o \
 	  i915_gem_stolen.o \
 	  i915_gem_tiling.o \
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index c511b3cbf9b2..9ffb4b7eebd9 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -39,6 +39,7 @@
 #include "intel_lrc.h"
 #include "i915_gem_gtt.h"
 #include "i915_gem_render_state.h"
+#include "i915_gem_request.h"
 #include <linux/io-mapping.h>
 #include <linux/i2c.h>
 #include <linux/i2c-algo-bit.h>
@@ -2154,170 +2155,6 @@ void i915_gem_track_fb(struct drm_i915_gem_object *old,
 		       struct drm_i915_gem_object *new,
 		       unsigned frontbuffer_bits);
 
-/**
- * Request queue structure.
- *
- * The request queue allows us to note sequence numbers that have been emitted
- * and may be associated with active buffers to be retired.
- *
- * By keeping this list, we can avoid having to do questionable sequence
- * number comparisons on buffer last_read|write_seqno. It also allows an
- * emission time to be associated with the request for tracking how far ahead
- * of the GPU the submission is.
- *
- * The requests are reference counted, so upon creation they should have an
- * initial reference taken using kref_init
- */
-struct drm_i915_gem_request {
-	struct kref ref;
-
-	/** On Which ring this request was generated */
-	struct drm_i915_private *i915;
-	struct intel_engine_cs *ring;
-	unsigned reset_counter;
-
-	 /** GEM sequence number associated with the previous request,
-	  * when the HWS breadcrumb is equal to this the GPU is processing
-	  * this request.
-	  */
-	u32 previous_seqno;
-
-	 /** GEM sequence number associated with this request,
-	  * when the HWS breadcrumb is equal or greater than this the GPU
-	  * has finished processing this request.
-	  */
-	u32 seqno;
-
-	/** Position in the ringbuffer of the start of the request */
-	u32 head;
-
-	/**
-	 * Position in the ringbuffer of the start of the postfix.
-	 * This is required to calculate the maximum available ringbuffer
-	 * space without overwriting the postfix.
-	 */
-	 u32 postfix;
-
-	/** Position in the ringbuffer of the end of the whole request */
-	u32 tail;
-
-	/**
-	 * Context and ring buffer related to this request
-	 * Contexts are refcounted, so when this request is associated with a
-	 * context, we must increment the context's refcount, to guarantee that
-	 * it persists while any request is linked to it. Requests themselves
-	 * are also refcounted, so the request will only be freed when the last
-	 * reference to it is dismissed, and the code in
-	 * i915_gem_request_free() will then decrement the refcount on the
-	 * context.
-	 */
-	struct intel_context *ctx;
-	struct intel_ringbuffer *ringbuf;
-
-	/** Batch buffer related to this request if any (used for
-	    error state dump only) */
-	struct drm_i915_gem_object *batch_obj;
-
-	/** Time at which this request was emitted, in jiffies. */
-	unsigned long emitted_jiffies;
-
-	/** global list entry for this request */
-	struct list_head list;
-
-	struct drm_i915_file_private *file_priv;
-	/** file_priv list entry for this request */
-	struct list_head client_list;
-
-	/** process identifier submitting this request */
-	struct pid *pid;
-
-	/**
-	 * The ELSP only accepts two elements at a time, so we queue
-	 * context/tail pairs on a given queue (ring->execlist_queue) until the
-	 * hardware is available. The queue serves a double purpose: we also use
-	 * it to keep track of the up to 2 contexts currently in the hardware
-	 * (usually one in execution and the other queued up by the GPU): We
-	 * only remove elements from the head of the queue when the hardware
-	 * informs us that an element has been completed.
-	 *
-	 * All accesses to the queue are mediated by a spinlock
-	 * (ring->execlist_lock).
-	 */
-
-	/** Execlist link in the submission queue.*/
-	struct list_head execlist_link;
-
-	/** Execlists no. of times this request has been sent to the ELSP */
-	int elsp_submitted;
-
-};
-
-int i915_gem_request_alloc(struct intel_engine_cs *ring,
-			   struct intel_context *ctx,
-			   struct drm_i915_gem_request **req_out);
-void i915_gem_request_cancel(struct drm_i915_gem_request *req);
-void i915_gem_request_free(struct kref *req_ref);
-int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
-				   struct drm_file *file);
-
-static inline uint32_t
-i915_gem_request_get_seqno(struct drm_i915_gem_request *req)
-{
-	return req ? req->seqno : 0;
-}
-
-static inline struct intel_engine_cs *
-i915_gem_request_get_ring(struct drm_i915_gem_request *req)
-{
-	return req ? req->ring : NULL;
-}
-
-static inline struct drm_i915_gem_request *
-i915_gem_request_reference(struct drm_i915_gem_request *req)
-{
-	if (req)
-		kref_get(&req->ref);
-	return req;
-}
-
-static inline void
-i915_gem_request_unreference(struct drm_i915_gem_request *req)
-{
-	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
-	kref_put(&req->ref, i915_gem_request_free);
-}
-
-static inline void
-i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
-{
-	struct drm_device *dev;
-
-	if (!req)
-		return;
-
-	dev = req->ring->dev;
-	if (kref_put_mutex(&req->ref, i915_gem_request_free, &dev->struct_mutex))
-		mutex_unlock(&dev->struct_mutex);
-}
-
-static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
-					   struct drm_i915_gem_request *src)
-{
-	if (src)
-		i915_gem_request_reference(src);
-
-	if (*pdst)
-		i915_gem_request_unreference(*pdst);
-
-	*pdst = src;
-}
-
-/*
- * XXX: i915_gem_request_completed should be here but currently needs the
- * definition of i915_seqno_passed() which is below. It will be moved in
- * a later patch when the call to i915_seqno_passed() is obsoleted...
- */
-
 /*
  * A command that requires special handling by the command parser.
  */
@@ -2966,27 +2803,6 @@ int i915_gem_dumb_create(struct drm_file *file_priv,
 			 struct drm_mode_create_dumb *args);
 int i915_gem_mmap_gtt(struct drm_file *file_priv, struct drm_device *dev,
 		      uint32_t handle, uint64_t *offset);
-/**
- * Returns true if seq1 is later than seq2.
- */
-static inline bool
-i915_seqno_passed(uint32_t seq1, uint32_t seq2)
-{
-	return (int32_t)(seq1 - seq2) >= 0;
-}
-
-static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
-{
-	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
-				 req->previous_seqno);
-}
-
-static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
-{
-	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
-				 req->seqno);
-}
-
 int __must_check i915_gem_get_seqno(struct drm_device *dev, u32 *seqno);
 int __must_check i915_gem_set_seqno(struct drm_device *dev, u32 seqno);
 
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 2e87639ecd1e..a23dea27f272 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1105,389 +1105,6 @@ put_rpm:
 	return ret;
 }
 
-static int
-i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
-{
-	if (__i915_terminally_wedged(reset_counter))
-		return -EIO;
-
-	if (__i915_reset_in_progress(reset_counter)) {
-		/* Non-interruptible callers can't handle -EAGAIN, hence return
-		 * -EIO unconditionally for these. */
-		if (!interruptible)
-			return -EIO;
-
-		return -EAGAIN;
-	}
-
-	return 0;
-}
-
-static unsigned long local_clock_us(unsigned *cpu)
-{
-	unsigned long t;
-
-	/* Cheaply and approximately convert from nanoseconds to microseconds.
-	 * The result and subsequent calculations are also defined in the same
-	 * approximate microseconds units. The principal source of timing
-	 * error here is from the simple truncation.
-	 *
-	 * Note that local_clock() is only defined wrt to the current CPU;
-	 * the comparisons are no longer valid if we switch CPUs. Instead of
-	 * blocking preemption for the entire busywait, we can detect the CPU
-	 * switch and use that as indicator of system load and a reason to
-	 * stop busywaiting, see busywait_stop().
-	 */
-	*cpu = get_cpu();
-	t = local_clock() >> 10;
-	put_cpu();
-
-	return t;
-}
-
-static bool busywait_stop(unsigned long timeout, unsigned cpu)
-{
-	unsigned this_cpu;
-
-	if (time_after(local_clock_us(&this_cpu), timeout))
-		return true;
-
-	return this_cpu != cpu;
-}
-
-static bool __i915_spin_request(struct drm_i915_gem_request *req,
-				struct intel_wait *wait,
-				int state)
-{
-	unsigned long timeout;
-	unsigned cpu;
-
-	/* When waiting for high frequency requests, e.g. during synchronous
-	 * rendering split between the CPU and GPU, the finite amount of time
-	 * required to set up the irq and wait upon it limits the response
-	 * rate. By busywaiting on the request completion for a short while we
-	 * can service the high frequency waits as quick as possible. However,
-	 * if it is a slow request, we want to sleep as quickly as possible.
-	 * The tradeoff between waiting and sleeping is roughly the time it
-	 * takes to sleep on a request, on the order of a microsecond.
-	 */
-
-	/* Only spin if we know the GPU is processing this request */
-	if (!i915_gem_request_started(req))
-		return false;
-
-	timeout = local_clock_us(&cpu) + 5;
-	do {
-		if (i915_gem_request_completed(req))
-			return true;
-
-		if (signal_pending_state(state, wait->task))
-			break;
-
-		if (busywait_stop(timeout, cpu))
-			break;
-
-		cpu_relax_lowlatency();
-
-		/* Break the loop if we have consumed the timeslice (or been
-		 * preempted) or when either the background thread has
-		 * enabled the interrupt, or the IRQ has fired.
-		 */
-	} while (!need_resched() && wait->task->state == state);
-
-	return false;
-}
-
-/**
- * __i915_wait_request - wait until execution of request has finished
- * @req: duh!
- * @interruptible: do an interruptible wait (normally yes)
- * @timeout: in - how long to wait (NULL forever); out - how much time remaining
- *
- * Note: It is of utmost importance that the passed in seqno and reset_counter
- * values have been read by the caller in an smp safe manner. Where read-side
- * locks are involved, it is sufficient to read the reset_counter before
- * unlocking the lock that protects the seqno. For lockless tricks, the
- * reset_counter _must_ be read before, and an appropriate smp_rmb must be
- * inserted.
- *
- * Returns 0 if the request was found within the alloted time. Else returns the
- * errno with remaining time filled in timeout argument.
- */
-int __i915_wait_request(struct drm_i915_gem_request *req,
-			bool interruptible,
-			s64 *timeout,
-			struct intel_rps_client *rps)
-{
-	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
-	struct intel_wait wait;
-	unsigned long timeout_remain;
-	int ret = 0;
-
-	might_sleep();
-
-	if (list_empty(&req->list))
-		return 0;
-
-	if (i915_gem_request_completed(req))
-		return 0;
-
-	timeout_remain = MAX_SCHEDULE_TIMEOUT;
-	if (timeout) {
-		if (WARN_ON(*timeout < 0))
-			return -EINVAL;
-
-		if (*timeout == 0)
-			return -ETIME;
-
-		/* Record current time in case interrupted, or wedged */
-		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
-		*timeout += ktime_get_raw_ns();
-	}
-
-	trace_i915_gem_request_wait_begin(req);
-
-	/* This client is about to stall waiting for the GPU. In many cases
-	 * this is undesirable and limits the throughput of the system, as
-	 * many clients cannot continue processing user input/output whilst
-	 * blocked. RPS autotuning may take tens of milliseconds to respond
-	 * to the GPU load and thus incurs additional latency for the client.
-	 * We can circumvent that by promoting the GPU frequency to maximum
-	 * before we wait. This makes the GPU throttle up much more quickly
-	 * (good for benchmarks and user experience, e.g. window animations),
-	 * but at a cost of spending more power processing the workload
-	 * (bad for battery). Not all clients even want their results
-	 * immediately and for them we should just let the GPU select its own
-	 * frequency to maximise efficiency. To prevent a single client from
-	 * forcing the clocks too high for the whole system, we only allow
-	 * each client to waitboost once in a busy period.
-	 */
-	if (INTEL_INFO(req->i915)->gen >= 6)
-		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
-
-	intel_wait_init(&wait, req->seqno);
-	set_task_state(wait.task, state);
-
-	/* Optimistic spin for the next ~jiffie before touching IRQs */
-	if (intel_engine_add_wait(req->ring, &wait)) {
-		if (__i915_spin_request(req, &wait, state))
-			goto out;
-
-		intel_engine_enable_irq(req->ring);
-
-		/* In order to check that we haven't missed the interrupt
-		 * as we enabled it, we need to kick ourselves to do a
-		 * coherent check on the seqno before we sleep.
-		 */
-		goto wakeup;
-	}
-
-	for (;;) {
-		if (signal_pending_state(state, wait.task)) {
-			ret = -ERESTARTSYS;
-			break;
-		}
-
-		/* Ensure that even if the GPU hangs, we get woken up. */
-		i915_queue_hangcheck(req->i915);
-
-		timeout_remain = io_schedule_timeout(timeout_remain);
-		if (timeout_remain == 0) {
-			ret = -ETIME;
-			break;
-		}
-
-		if (intel_wait_complete(&wait))
-			break;
-
-wakeup:		set_task_state(wait.task, state);
-
-		/* Before we do the heavier coherent read of the seqno,
-		 * check the value (hopefully) in the CPU cacheline.
-		 */
-		if (i915_gem_request_completed(req))
-			break;
-
-		/* Ensure our read of the seqno is coherent so that we
-		 * do not "miss an interrupt" (i.e. if this is the last
-		 * request and the seqno write from the GPU is not visible
-		 * by the time the interrupt fires, we will see that the
-		 * request is incomplete and go back to sleep awaiting
-		 * another interrupt that will never come.)
-		 *
-		 * Strictly, we only need to do this once after an interrupt,
-		 * but it is easier and safer to do it every time the waiter
-		 * is woken.
-		 */
-		if (req->ring->seqno_barrier) {
-			req->ring->seqno_barrier(req->ring);
-			if (i915_gem_request_completed(req))
-				break;
-		}
-
-		/* We need to check whether any gpu reset happened in between
-		 * the request being submitted and now. If a reset has occurred,
-		 * the request is effectively complete (we either are in the
-		 * process of or have discarded the rendering and completely
-		 * reset the GPU. The results of the request are lost and we
-		 * are free to continue on with the original operation.
-		 */
-		if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
-			break;
-	}
-out:
-	intel_engine_remove_wait(req->ring, &wait);
-	__set_task_state(wait.task, TASK_RUNNING);
-	trace_i915_gem_request_wait_end(req);
-
-	if (timeout) {
-		*timeout -= ktime_get_raw_ns();
-		if (*timeout < 0)
-			*timeout = 0;
-
-		/*
-		 * Apparently ktime isn't accurate enough and occasionally has a
-		 * bit of mismatch in the jiffies<->nsecs<->ktime loop. So patch
-		 * things up to make the test happy. We allow up to 1 jiffy.
-		 *
-		 * This is a regrssion from the timespec->ktime conversion.
-		 */
-		if (ret == -ETIME && *timeout < jiffies_to_usecs(1)*1000)
-			*timeout = 0;
-	}
-
-	if (ret == 0 && rps && req->seqno == req->ring->last_submitted_seqno) {
-		/* The GPU is now idle and this client has stalled.
-		 * Since no other client has submitted a request in the
-		 * meantime, assume that this client is the only one
-		 * supplying work to the GPU but is unable to keep that
-		 * work supplied because it is waiting. Since the GPU is
-		 * then never kept fully busy, RPS autoclocking will
-		 * keep the clocks relatively low, causing further delays.
-		 * Compensate by giving the synchronous client credit for
-		 * a waitboost next time.
-		 */
-		spin_lock(&req->i915->rps.client_lock);
-		list_del_init(&rps->link);
-		spin_unlock(&req->i915->rps.client_lock);
-	}
-
-	return ret;
-}
-
-int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
-				   struct drm_file *file)
-{
-	struct drm_i915_private *dev_private;
-	struct drm_i915_file_private *file_priv;
-
-	WARN_ON(!req || !file || req->file_priv);
-
-	if (!req || !file)
-		return -EINVAL;
-
-	if (req->file_priv)
-		return -EINVAL;
-
-	dev_private = req->ring->dev->dev_private;
-	file_priv = file->driver_priv;
-
-	spin_lock(&file_priv->mm.lock);
-	req->file_priv = file_priv;
-	list_add_tail(&req->client_list, &file_priv->mm.request_list);
-	spin_unlock(&file_priv->mm.lock);
-
-	req->pid = get_pid(task_pid(current));
-
-	return 0;
-}
-
-static inline void
-i915_gem_request_remove_from_client(struct drm_i915_gem_request *request)
-{
-	struct drm_i915_file_private *file_priv = request->file_priv;
-
-	if (!file_priv)
-		return;
-
-	spin_lock(&file_priv->mm.lock);
-	list_del(&request->client_list);
-	request->file_priv = NULL;
-	spin_unlock(&file_priv->mm.lock);
-
-	put_pid(request->pid);
-	request->pid = NULL;
-}
-
-static void i915_gem_request_retire(struct drm_i915_gem_request *request)
-{
-	trace_i915_gem_request_retire(request);
-
-	/* We know the GPU must have read the request to have
-	 * sent us the seqno + interrupt, so use the position
-	 * of tail of the request to update the last known position
-	 * of the GPU head.
-	 *
-	 * Note this requires that we are always called in request
-	 * completion order.
-	 */
-	request->ringbuf->last_retired_head = request->postfix;
-
-	list_del_init(&request->list);
-	i915_gem_request_remove_from_client(request);
-
-	i915_gem_request_unreference(request);
-}
-
-static void
-__i915_gem_request_retire__upto(struct drm_i915_gem_request *req)
-{
-	struct intel_engine_cs *engine = req->ring;
-	struct drm_i915_gem_request *tmp;
-
-	lockdep_assert_held(&engine->dev->struct_mutex);
-
-	if (list_empty(&req->list))
-		return;
-
-	do {
-		tmp = list_first_entry(&engine->request_list,
-				       typeof(*tmp), list);
-
-		i915_gem_request_retire(tmp);
-	} while (tmp != req);
-
-	WARN_ON(i915_verify_lists(engine->dev));
-}
-
-/**
- * Waits for a request to be signaled, and cleans up the
- * request and object lists appropriately for that event.
- */
-int
-i915_wait_request(struct drm_i915_gem_request *req)
-{
-	struct drm_device *dev;
-	struct drm_i915_private *dev_priv;
-	bool interruptible;
-	int ret;
-
-	BUG_ON(req == NULL);
-
-	dev = req->ring->dev;
-	dev_priv = dev->dev_private;
-	interruptible = dev_priv->mm.interruptible;
-
-	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
-
-	ret = __i915_wait_request(req, interruptible, NULL, NULL);
-	if (ret)
-		return ret;
-
-	__i915_gem_request_retire__upto(req);
-	return 0;
-}
-
 /**
  * Ensures that all rendering to the object has completed and the object is
  * safe to unbind from the GTT or access from the CPU.
@@ -1541,7 +1158,7 @@ i915_gem_object_retire_request(struct drm_i915_gem_object *obj,
 	else if (obj->last_write_req == req)
 		i915_gem_object_retire__write(obj);
 
-	__i915_gem_request_retire__upto(req);
+	i915_gem_request_retire__upto(req);
 }
 
 /* A nonblocking variant of the above wait. This is a highly dangerous routine
@@ -2696,109 +2313,6 @@ static void i915_set_reset_status(struct drm_i915_private *dev_priv,
 	}
 }
 
-void i915_gem_request_free(struct kref *req_ref)
-{
-	struct drm_i915_gem_request *req = container_of(req_ref,
-						 typeof(*req), ref);
-	struct intel_context *ctx = req->ctx;
-
-	if (req->file_priv)
-		i915_gem_request_remove_from_client(req);
-
-	if (ctx) {
-		if (i915.enable_execlists) {
-			if (ctx != req->ring->default_context)
-				intel_lr_context_unpin(req);
-		}
-
-		i915_gem_context_unreference(ctx);
-	}
-
-	kmem_cache_free(req->i915->requests, req);
-}
-
-int i915_gem_request_alloc(struct intel_engine_cs *ring,
-			   struct intel_context *ctx,
-			   struct drm_i915_gem_request **req_out)
-{
-	struct drm_i915_private *dev_priv = to_i915(ring->dev);
-	unsigned reset_counter = i915_reset_counter(&dev_priv->gpu_error);
-	struct drm_i915_gem_request *req;
-	int ret;
-
-	if (!req_out)
-		return -EINVAL;
-
-	*req_out = NULL;
-
-	/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
-	 * EIO if the GPU is already wedged, or EAGAIN to drop the struct_mutex
-	 * and restart.
-	 */
-	ret = i915_gem_check_wedge(reset_counter, dev_priv->mm.interruptible);
-	if (ret)
-		return ret;
-
-	req = kmem_cache_zalloc(dev_priv->requests, GFP_KERNEL);
-	if (req == NULL)
-		return -ENOMEM;
-
-	ret = i915_gem_get_seqno(ring->dev, &req->seqno);
-	if (ret)
-		goto err;
-
-	kref_init(&req->ref);
-	req->i915 = dev_priv;
-	req->ring = ring;
-	req->reset_counter = reset_counter;
-	req->ctx  = ctx;
-	i915_gem_context_reference(req->ctx);
-
-	if (i915.enable_execlists)
-		ret = intel_logical_ring_alloc_request_extras(req);
-	else
-		ret = intel_ring_alloc_request_extras(req);
-	if (ret) {
-		i915_gem_context_unreference(req->ctx);
-		goto err;
-	}
-
-	/*
-	 * Reserve space in the ring buffer for all the commands required to
-	 * eventually emit this request. This is to guarantee that the
-	 * i915_add_request() call can't fail. Note that the reserve may need
-	 * to be redone if the request is not actually submitted straight
-	 * away, e.g. because a GPU scheduler has deferred it.
-	 */
-	if (i915.enable_execlists)
-		ret = intel_logical_ring_reserve_space(req);
-	else
-		ret = intel_ring_reserve_space(req);
-	if (ret) {
-		/*
-		 * At this point, the request is fully allocated even if not
-		 * fully prepared. Thus it can be cleaned up using the proper
-		 * free code.
-		 */
-		i915_gem_request_cancel(req);
-		return ret;
-	}
-
-	*req_out = req;
-	return 0;
-
-err:
-	kmem_cache_free(dev_priv->requests, req);
-	return ret;
-}
-
-void i915_gem_request_cancel(struct drm_i915_gem_request *req)
-{
-	intel_ring_reserved_space_cancel(req->ringbuf);
-
-	i915_gem_request_unreference(req);
-}
-
 struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *ring)
 {
@@ -2882,14 +2396,14 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
 	 * implicit references on things like e.g. ppgtt address spaces through
 	 * the request.
 	 */
-	while (!list_empty(&ring->request_list)) {
+	if (!list_empty(&ring->request_list)) {
 		struct drm_i915_gem_request *request;
 
-		request = list_first_entry(&ring->request_list,
-					   struct drm_i915_gem_request,
-					   list);
+		request = list_last_entry(&ring->request_list,
+					  struct drm_i915_gem_request,
+					  list);
 
-		i915_gem_request_retire(request);
+		i915_gem_request_retire__upto(request);
 	}
 
 	/* Having flushed all requests from all queues, we know that all
@@ -2954,7 +2468,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 		if (!i915_gem_request_completed(request))
 			break;
 
-		i915_gem_request_retire(request);
+		i915_gem_request_retire__upto(request);
 	}
 
 	/* Move any buffers on the active list that are no longer referenced
@@ -3077,7 +2591,7 @@ i915_gem_object_flush_active(struct drm_i915_gem_object *obj)
 			goto retire;
 
 		if (i915_gem_request_completed(req)) {
-			__i915_gem_request_retire__upto(req);
+			i915_gem_request_retire__upto(req);
 retire:
 			i915_gem_object_retire__read(obj, i);
 		}
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
new file mode 100644
index 000000000000..28435c8d7b1f
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -0,0 +1,513 @@
+/*
+ * Copyright © 2008-2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#include "i915_drv.h"
+
+static int
+i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
+{
+	if (__i915_terminally_wedged(reset_counter))
+		return -EIO;
+
+	if (__i915_reset_in_progress(reset_counter)) {
+		/* Non-interruptible callers can't handle -EAGAIN, hence return
+		 * -EIO unconditionally for these. */
+		if (!interruptible)
+			return -EIO;
+
+		return -EAGAIN;
+	}
+
+	return 0;
+}
+
+int i915_gem_request_alloc(struct intel_engine_cs *ring,
+			   struct intel_context *ctx,
+			   struct drm_i915_gem_request **req_out)
+{
+	struct drm_i915_private *dev_priv = to_i915(ring->dev);
+	unsigned reset_counter = i915_reset_counter(&dev_priv->gpu_error);
+	struct drm_i915_gem_request *req;
+	int ret;
+
+	if (!req_out)
+		return -EINVAL;
+
+	*req_out = NULL;
+
+	/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
+	 * EIO if the GPU is already wedged, or EAGAIN to drop the struct_mutex
+	 * and restart.
+	 */
+	ret = i915_gem_check_wedge(reset_counter, dev_priv->mm.interruptible);
+	if (ret)
+		return ret;
+
+	req = kmem_cache_zalloc(dev_priv->requests, GFP_KERNEL);
+	if (req == NULL)
+		return -ENOMEM;
+
+	ret = i915_gem_get_seqno(ring->dev, &req->seqno);
+	if (ret)
+		goto err;
+
+	kref_init(&req->ref);
+	req->i915 = dev_priv;
+	req->ring = ring;
+	req->reset_counter = reset_counter;
+	req->ctx  = ctx;
+	i915_gem_context_reference(req->ctx);
+
+	if (i915.enable_execlists)
+		ret = intel_logical_ring_alloc_request_extras(req);
+	else
+		ret = intel_ring_alloc_request_extras(req);
+	if (ret) {
+		i915_gem_context_unreference(req->ctx);
+		goto err;
+	}
+
+	/*
+	 * Reserve space in the ring buffer for all the commands required to
+	 * eventually emit this request. This is to guarantee that the
+	 * i915_add_request() call can't fail. Note that the reserve may need
+	 * to be redone if the request is not actually submitted straight
+	 * away, e.g. because a GPU scheduler has deferred it.
+	 */
+	if (i915.enable_execlists)
+		ret = intel_logical_ring_reserve_space(req);
+	else
+		ret = intel_ring_reserve_space(req);
+	if (ret) {
+		/*
+		 * At this point, the request is fully allocated even if not
+		 * fully prepared. Thus it can be cleaned up using the proper
+		 * free code.
+		 */
+		i915_gem_request_cancel(req);
+		return ret;
+	}
+
+	*req_out = req;
+	return 0;
+
+err:
+	kmem_cache_free(dev_priv->requests, req);
+	return ret;
+}
+
+void i915_gem_request_cancel(struct drm_i915_gem_request *req)
+{
+	intel_ring_reserved_space_cancel(req->ringbuf);
+
+	i915_gem_request_unreference(req);
+}
+
+int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
+				   struct drm_file *file)
+{
+	struct drm_i915_private *dev_private;
+	struct drm_i915_file_private *file_priv;
+
+	WARN_ON(!req || !file || req->file_priv);
+
+	if (!req || !file)
+		return -EINVAL;
+
+	if (req->file_priv)
+		return -EINVAL;
+
+	dev_private = req->ring->dev->dev_private;
+	file_priv = file->driver_priv;
+
+	spin_lock(&file_priv->mm.lock);
+	req->file_priv = file_priv;
+	list_add_tail(&req->client_list, &file_priv->mm.request_list);
+	spin_unlock(&file_priv->mm.lock);
+
+	req->pid = get_pid(task_pid(current));
+
+	return 0;
+}
+
+static inline void
+i915_gem_request_remove_from_client(struct drm_i915_gem_request *request)
+{
+	struct drm_i915_file_private *file_priv = request->file_priv;
+
+	if (!file_priv)
+		return;
+
+	spin_lock(&file_priv->mm.lock);
+	list_del(&request->client_list);
+	request->file_priv = NULL;
+	spin_unlock(&file_priv->mm.lock);
+
+	put_pid(request->pid);
+	request->pid = NULL;
+}
+
+static void i915_gem_request_retire(struct drm_i915_gem_request *request)
+{
+	trace_i915_gem_request_retire(request);
+
+	/* We know the GPU must have read the request to have
+	 * sent us the seqno + interrupt, so use the position
+	 * of tail of the request to update the last known position
+	 * of the GPU head.
+	 *
+	 * Note this requires that we are always called in request
+	 * completion order.
+	 */
+	request->ringbuf->last_retired_head = request->postfix;
+
+	list_del_init(&request->list);
+	i915_gem_request_remove_from_client(request);
+
+	i915_gem_request_unreference(request);
+}
+
+void
+i915_gem_request_retire__upto(struct drm_i915_gem_request *req)
+{
+	struct intel_engine_cs *engine = req->ring;
+	struct drm_i915_gem_request *tmp;
+
+	lockdep_assert_held(&engine->dev->struct_mutex);
+
+	if (list_empty(&req->list))
+		return;
+
+	do {
+		tmp = list_first_entry(&engine->request_list,
+				       typeof(*tmp), list);
+
+		i915_gem_request_retire(tmp);
+	} while (tmp != req);
+
+	WARN_ON(i915_verify_lists(engine->dev));
+}
+
+static unsigned long local_clock_us(unsigned *cpu)
+{
+	unsigned long t;
+
+	/* Cheaply and approximately convert from nanoseconds to microseconds.
+	 * The result and subsequent calculations are also defined in the same
+	 * approximate microseconds units. The principal source of timing
+	 * error here is from the simple truncation.
+	 *
+	 * Note that local_clock() is only defined wrt to the current CPU;
+	 * the comparisons are no longer valid if we switch CPUs. Instead of
+	 * blocking preemption for the entire busywait, we can detect the CPU
+	 * switch and use that as indicator of system load and a reason to
+	 * stop busywaiting, see busywait_stop().
+	 */
+	*cpu = get_cpu();
+	t = local_clock() >> 10;
+	put_cpu();
+
+	return t;
+}
+
+static bool busywait_stop(unsigned long timeout, unsigned cpu)
+{
+	unsigned this_cpu;
+
+	if (time_after(local_clock_us(&this_cpu), timeout))
+		return true;
+
+	return this_cpu != cpu;
+}
+
+static bool __i915_spin_request(struct drm_i915_gem_request *req,
+				struct intel_wait *wait,
+				int state)
+{
+	unsigned long timeout;
+	unsigned cpu;
+
+	/* When waiting for high frequency requests, e.g. during synchronous
+	 * rendering split between the CPU and GPU, the finite amount of time
+	 * required to set up the irq and wait upon it limits the response
+	 * rate. By busywaiting on the request completion for a short while we
+	 * can service the high frequency waits as quick as possible. However,
+	 * if it is a slow request, we want to sleep as quickly as possible.
+	 * The tradeoff between waiting and sleeping is roughly the time it
+	 * takes to sleep on a request, on the order of a microsecond.
+	 */
+
+	/* Only spin if we know the GPU is processing this request */
+	if (!i915_gem_request_started(req))
+		return false;
+
+	timeout = local_clock_us(&cpu) + 5;
+	do {
+		if (i915_gem_request_completed(req))
+			return true;
+
+		if (signal_pending_state(state, wait->task))
+			break;
+
+		if (busywait_stop(timeout, cpu))
+			break;
+
+		cpu_relax_lowlatency();
+
+		/* Break the loop if we have consumed the timeslice (or been
+		 * preempted) or when either the background thread has
+		 * enabled the interrupt, or the IRQ has fired.
+		 */
+	} while (!need_resched() && wait->task->state == state);
+
+	return false;
+}
+
+/**
+ * __i915_wait_request - wait until execution of request has finished
+ * @req: duh!
+ * @interruptible: do an interruptible wait (normally yes)
+ * @timeout: in - how long to wait (NULL forever); out - how much time remaining
+ *
+ * Note: It is of utmost importance that the passed in seqno and reset_counter
+ * values have been read by the caller in an smp safe manner. Where read-side
+ * locks are involved, it is sufficient to read the reset_counter before
+ * unlocking the lock that protects the seqno. For lockless tricks, the
+ * reset_counter _must_ be read before, and an appropriate smp_rmb must be
+ * inserted.
+ *
+ * Returns 0 if the request was found within the alloted time. Else returns the
+ * errno with remaining time filled in timeout argument.
+ */
+int __i915_wait_request(struct drm_i915_gem_request *req,
+			bool interruptible,
+			s64 *timeout,
+			struct intel_rps_client *rps)
+{
+	int state = interruptible ? TASK_INTERRUPTIBLE : TASK_UNINTERRUPTIBLE;
+	struct intel_wait wait;
+	unsigned long timeout_remain;
+	int ret = 0;
+
+	might_sleep();
+
+	if (list_empty(&req->list))
+		return 0;
+
+	if (i915_gem_request_completed(req))
+		return 0;
+
+	timeout_remain = MAX_SCHEDULE_TIMEOUT;
+	if (timeout) {
+		if (WARN_ON(*timeout < 0))
+			return -EINVAL;
+
+		if (*timeout == 0)
+			return -ETIME;
+
+		/* Record current time in case interrupted, or wedged */
+		timeout_remain = nsecs_to_jiffies_timeout(*timeout);
+		*timeout += ktime_get_raw_ns();
+	}
+
+	trace_i915_gem_request_wait_begin(req);
+
+	/* This client is about to stall waiting for the GPU. In many cases
+	 * this is undesirable and limits the throughput of the system, as
+	 * many clients cannot continue processing user input/output whilst
+	 * blocked. RPS autotuning may take tens of milliseconds to respond
+	 * to the GPU load and thus incurs additional latency for the client.
+	 * We can circumvent that by promoting the GPU frequency to maximum
+	 * before we wait. This makes the GPU throttle up much more quickly
+	 * (good for benchmarks and user experience, e.g. window animations),
+	 * but at a cost of spending more power processing the workload
+	 * (bad for battery). Not all clients even want their results
+	 * immediately and for them we should just let the GPU select its own
+	 * frequency to maximise efficiency. To prevent a single client from
+	 * forcing the clocks too high for the whole system, we only allow
+	 * each client to waitboost once in a busy period.
+	 */
+	if (INTEL_INFO(req->i915)->gen >= 6)
+		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
+
+	intel_wait_init(&wait, req->seqno);
+	set_task_state(wait.task, state);
+
+	/* Optimistic spin for the next ~jiffie before touching IRQs */
+	if (intel_engine_add_wait(req->ring, &wait)) {
+		if (__i915_spin_request(req, &wait, state))
+			goto out;
+
+		intel_engine_enable_irq(req->ring);
+
+		/* In order to check that we haven't missed the interrupt
+		 * as we enabled it, we need to kick ourselves to do a
+		 * coherent check on the seqno before we sleep.
+		 */
+		goto wakeup;
+	}
+
+	for (;;) {
+		if (signal_pending_state(state, wait.task)) {
+			ret = -ERESTARTSYS;
+			break;
+		}
+
+		/* Ensure that even if the GPU hangs, we get woken up. */
+		i915_queue_hangcheck(req->i915);
+
+		timeout_remain = io_schedule_timeout(timeout_remain);
+		if (timeout_remain == 0) {
+			ret = -ETIME;
+			break;
+		}
+
+		if (intel_wait_complete(&wait))
+			break;
+
+wakeup:		set_task_state(wait.task, state);
+
+		/* Before we do the heavier coherent read of the seqno,
+		 * check the value (hopefully) in the CPU cacheline.
+		 */
+		if (i915_gem_request_completed(req))
+			break;
+
+		/* Ensure our read of the seqno is coherent so that we
+		 * do not "miss an interrupt" (i.e. if this is the last
+		 * request and the seqno write from the GPU is not visible
+		 * by the time the interrupt fires, we will see that the
+		 * request is incomplete and go back to sleep awaiting
+		 * another interrupt that will never come.)
+		 *
+		 * Strictly, we only need to do this once after an interrupt,
+		 * but it is easier and safer to do it every time the waiter
+		 * is woken.
+		 */
+		if (req->ring->seqno_barrier) {
+			req->ring->seqno_barrier(req->ring);
+			if (i915_gem_request_completed(req))
+				break;
+		}
+
+		/* We need to check whether any gpu reset happened in between
+		 * the request being submitted and now. If a reset has occurred,
+		 * the request is effectively complete (we either are in the
+		 * process of or have discarded the rendering and completely
+		 * reset the GPU. The results of the request are lost and we
+		 * are free to continue on with the original operation.
+		 */
+		if (req->reset_counter != i915_reset_counter(&req->i915->gpu_error))
+			break;
+	}
+out:
+	intel_engine_remove_wait(req->ring, &wait);
+	__set_task_state(wait.task, TASK_RUNNING);
+	trace_i915_gem_request_wait_end(req);
+
+	if (timeout) {
+		*timeout -= ktime_get_raw_ns();
+		if (*timeout < 0)
+			*timeout = 0;
+
+		/*
+		 * Apparently ktime isn't accurate enough and occasionally has a
+		 * bit of mismatch in the jiffies<->nsecs<->ktime loop. So patch
+		 * things up to make the test happy. We allow up to 1 jiffy.
+		 *
+		 * This is a regrssion from the timespec->ktime conversion.
+		 */
+		if (ret == -ETIME && *timeout < jiffies_to_usecs(1)*1000)
+			*timeout = 0;
+	}
+
+	if (ret == 0 && rps && req->seqno == req->ring->last_submitted_seqno) {
+		/* The GPU is now idle and this client has stalled.
+		 * Since no other client has submitted a request in the
+		 * meantime, assume that this client is the only one
+		 * supplying work to the GPU but is unable to keep that
+		 * work supplied because it is waiting. Since the GPU is
+		 * then never kept fully busy, RPS autoclocking will
+		 * keep the clocks relatively low, causing further delays.
+		 * Compensate by giving the synchronous client credit for
+		 * a waitboost next time.
+		 */
+		spin_lock(&req->i915->rps.client_lock);
+		list_del_init(&rps->link);
+		spin_unlock(&req->i915->rps.client_lock);
+	}
+
+	return ret;
+}
+
+
+/**
+ * Waits for a request to be signaled, and cleans up the
+ * request and object lists appropriately for that event.
+ */
+int
+i915_wait_request(struct drm_i915_gem_request *req)
+{
+	struct drm_device *dev;
+	struct drm_i915_private *dev_priv;
+	bool interruptible;
+	int ret;
+
+	BUG_ON(req == NULL);
+
+	dev = req->ring->dev;
+	dev_priv = dev->dev_private;
+	interruptible = dev_priv->mm.interruptible;
+
+	BUG_ON(!mutex_is_locked(&dev->struct_mutex));
+
+	ret = __i915_wait_request(req, interruptible, NULL, NULL);
+	if (ret)
+		return ret;
+
+	i915_gem_request_retire__upto(req);
+	return 0;
+}
+
+void i915_gem_request_free(struct kref *req_ref)
+{
+	struct drm_i915_gem_request *req = container_of(req_ref,
+						 typeof(*req), ref);
+	struct intel_context *ctx = req->ctx;
+
+	if (req->file_priv)
+		i915_gem_request_remove_from_client(req);
+
+	if (ctx) {
+		if (i915.enable_execlists) {
+			if (ctx != req->ring->default_context)
+				intel_lr_context_unpin(req);
+		}
+
+		i915_gem_context_unreference(ctx);
+	}
+
+	kmem_cache_free(req->i915->requests, req);
+}
+
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
new file mode 100644
index 000000000000..75c9015c19dc
--- /dev/null
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -0,0 +1,209 @@
+/*
+ * Copyright © 2008-2015 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ */
+
+#ifndef I915_GEM_REQUEST_H
+#define I915_GEM_REQUEST_H
+
+/**
+ * Request queue structure.
+ *
+ * The request queue allows us to note sequence numbers that have been emitted
+ * and may be associated with active buffers to be retired.
+ *
+ * By keeping this list, we can avoid having to do questionable sequence
+ * number comparisons on buffer last_read|write_seqno. It also allows an
+ * emission time to be associated with the request for tracking how far ahead
+ * of the GPU the submission is.
+ *
+ * The requests are reference counted, so upon creation they should have an
+ * initial reference taken using kref_init
+ */
+struct drm_i915_gem_request {
+	struct kref ref;
+
+	/** On Which ring this request was generated */
+	struct drm_i915_private *i915;
+	struct intel_engine_cs *ring;
+	unsigned reset_counter;
+
+	 /** GEM sequence number associated with the previous request,
+	  * when the HWS breadcrumb is equal to this the GPU is processing
+	  * this request.
+	  */
+	u32 previous_seqno;
+
+	 /** GEM sequence number associated with this request,
+	  * when the HWS breadcrumb is equal or greater than this the GPU
+	  * has finished processing this request.
+	  */
+	u32 seqno;
+
+	/** Position in the ringbuffer of the start of the request */
+	u32 head;
+
+	/**
+	 * Position in the ringbuffer of the start of the postfix.
+	 * This is required to calculate the maximum available ringbuffer
+	 * space without overwriting the postfix.
+	 */
+	 u32 postfix;
+
+	/** Position in the ringbuffer of the end of the whole request */
+	u32 tail;
+
+	/**
+	 * Context and ring buffer related to this request
+	 * Contexts are refcounted, so when this request is associated with a
+	 * context, we must increment the context's refcount, to guarantee that
+	 * it persists while any request is linked to it. Requests themselves
+	 * are also refcounted, so the request will only be freed when the last
+	 * reference to it is dismissed, and the code in
+	 * i915_gem_request_free() will then decrement the refcount on the
+	 * context.
+	 */
+	struct intel_context *ctx;
+	struct intel_ringbuffer *ringbuf;
+
+	/** Batch buffer related to this request if any (used for
+	    error state dump only) */
+	struct drm_i915_gem_object *batch_obj;
+
+	/** Time at which this request was emitted, in jiffies. */
+	unsigned long emitted_jiffies;
+
+	/** global list entry for this request */
+	struct list_head list;
+
+	struct drm_i915_file_private *file_priv;
+	/** file_priv list entry for this request */
+	struct list_head client_list;
+
+	/** process identifier submitting this request */
+	struct pid *pid;
+
+	/**
+	 * The ELSP only accepts two elements at a time, so we queue
+	 * context/tail pairs on a given queue (ring->execlist_queue) until the
+	 * hardware is available. The queue serves a double purpose: we also use
+	 * it to keep track of the up to 2 contexts currently in the hardware
+	 * (usually one in execution and the other queued up by the GPU): We
+	 * only remove elements from the head of the queue when the hardware
+	 * informs us that an element has been completed.
+	 *
+	 * All accesses to the queue are mediated by a spinlock
+	 * (ring->execlist_lock).
+	 */
+
+	/** Execlist link in the submission queue.*/
+	struct list_head execlist_link;
+
+	/** Execlists no. of times this request has been sent to the ELSP */
+	int elsp_submitted;
+
+};
+
+int i915_gem_request_alloc(struct intel_engine_cs *ring,
+			   struct intel_context *ctx,
+			   struct drm_i915_gem_request **req_out);
+void i915_gem_request_cancel(struct drm_i915_gem_request *req);
+void i915_gem_request_free(struct kref *req_ref);
+int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
+				   struct drm_file *file);
+void i915_gem_request_retire__upto(struct drm_i915_gem_request *req);
+
+static inline uint32_t
+i915_gem_request_get_seqno(struct drm_i915_gem_request *req)
+{
+	return req ? req->seqno : 0;
+}
+
+static inline struct intel_engine_cs *
+i915_gem_request_get_ring(struct drm_i915_gem_request *req)
+{
+	return req ? req->ring : NULL;
+}
+
+static inline struct drm_i915_gem_request *
+i915_gem_request_reference(struct drm_i915_gem_request *req)
+{
+	if (req)
+		kref_get(&req->ref);
+	return req;
+}
+
+static inline void
+i915_gem_request_unreference(struct drm_i915_gem_request *req)
+{
+	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
+	kref_put(&req->ref, i915_gem_request_free);
+}
+
+static inline void
+i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
+{
+	struct drm_device *dev;
+
+	if (!req)
+		return;
+
+	dev = req->ring->dev;
+	if (kref_put_mutex(&req->ref, i915_gem_request_free, &dev->struct_mutex))
+		mutex_unlock(&dev->struct_mutex);
+}
+
+static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
+					   struct drm_i915_gem_request *src)
+{
+	if (src)
+		i915_gem_request_reference(src);
+
+	if (*pdst)
+		i915_gem_request_unreference(*pdst);
+
+	*pdst = src;
+}
+
+/**
+ * Returns true if seq1 is later than seq2.
+ */
+static inline bool
+i915_seqno_passed(uint32_t seq1, uint32_t seq2)
+{
+	return (int32_t)(seq1 - seq2) >= 0;
+}
+
+static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
+{
+	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
+				 req->previous_seqno);
+}
+
+static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
+{
+	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
+				 req->seqno);
+}
+
+
+#endif /* I915_GEM_REQUEST_H */
-- 
2.6.3

_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 2/3] drm/i915: Move releasing of the GEM request from free to retire/cancel

[Chris Wilson]

If we move the release of the GEM request (i.e. decoupling it from the
various lists used for client and context tracking) after it is complete
(either by the GPU retiring the request, or by the caller cancelling the
request), we can remove the requirement that the final unreference of
the GEM request need to be under the struct_mutex.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c          |  4 +--
 drivers/gpu/drm/i915/i915_gem_request.c  | 54 +++++++++++++++-----------------
 drivers/gpu/drm/i915/i915_gem_request.h  | 14 ---------
 drivers/gpu/drm/i915/intel_breadcrumbs.c |  2 +-
 drivers/gpu/drm/i915/intel_display.c     |  2 +-
 drivers/gpu/drm/i915/intel_pm.c          |  2 +-
 6 files changed, 30 insertions(+), 48 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a23dea27f272..d92950b56f2d 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2676,7 +2676,7 @@ i915_gem_wait_ioctl(struct drm_device *dev, void *data, struct drm_file *file)
 			ret = __i915_wait_request(req[i], true,
 						  args->timeout_ns > 0 ? &args->timeout_ns : NULL,
 						  to_rps_client(file));
-		i915_gem_request_unreference__unlocked(req[i]);
+		i915_gem_request_unreference(req[i]);
 	}
 	return ret;
 
@@ -3688,7 +3688,7 @@ i915_gem_ring_throttle(struct drm_device *dev, struct drm_file *file)
 	if (ret == 0)
 		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work, 0);
 
-	i915_gem_request_unreference__unlocked(target);
+	i915_gem_request_unreference(target);
 
 	return ret;
 }
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 28435c8d7b1f..bb88146dd90c 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -73,6 +73,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 		goto err;
 
 	kref_init(&req->ref);
+	INIT_LIST_HEAD(&req->list);
 	req->i915 = dev_priv;
 	req->ring = ring;
 	req->reset_counter = reset_counter;
@@ -117,13 +118,6 @@ err:
 	return ret;
 }
 
-void i915_gem_request_cancel(struct drm_i915_gem_request *req)
-{
-	intel_ring_reserved_space_cancel(req->ringbuf);
-
-	i915_gem_request_unreference(req);
-}
-
 int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
 				   struct drm_file *file)
 {
@@ -168,6 +162,27 @@ i915_gem_request_remove_from_client(struct drm_i915_gem_request *request)
 	request->pid = NULL;
 }
 
+static void __i915_gem_request_release(struct drm_i915_gem_request *request)
+{
+	list_del_init(&request->list);
+
+	i915_gem_request_remove_from_client(request);
+
+	if (i915.enable_execlists) {
+		if (request->ctx != request->ring->default_context)
+			intel_lr_context_unpin(request);
+	}
+	i915_gem_context_unreference(request->ctx);
+
+	i915_gem_request_unreference(request);
+}
+
+void i915_gem_request_cancel(struct drm_i915_gem_request *req)
+{
+	intel_ring_reserved_space_cancel(req->ringbuf);
+	__i915_gem_request_release(req);
+}
+
 static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 {
 	trace_i915_gem_request_retire(request);
@@ -181,11 +196,7 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 	 * completion order.
 	 */
 	request->ringbuf->last_retired_head = request->postfix;
-
-	list_del_init(&request->list);
-	i915_gem_request_remove_from_client(request);
-
-	i915_gem_request_unreference(request);
+	__i915_gem_request_release(request);
 }
 
 void
@@ -492,22 +503,7 @@ i915_wait_request(struct drm_i915_gem_request *req)
 
 void i915_gem_request_free(struct kref *req_ref)
 {
-	struct drm_i915_gem_request *req = container_of(req_ref,
-						 typeof(*req), ref);
-	struct intel_context *ctx = req->ctx;
-
-	if (req->file_priv)
-		i915_gem_request_remove_from_client(req);
-
-	if (ctx) {
-		if (i915.enable_execlists) {
-			if (ctx != req->ring->default_context)
-				intel_lr_context_unpin(req);
-		}
-
-		i915_gem_context_unreference(ctx);
-	}
-
+	struct drm_i915_gem_request *req =
+		container_of(req_ref, typeof(*req), ref);
 	kmem_cache_free(req->i915->requests, req);
 }
-
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
index 75c9015c19dc..b19160a1511a 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -155,23 +155,9 @@ i915_gem_request_reference(struct drm_i915_gem_request *req)
 static inline void
 i915_gem_request_unreference(struct drm_i915_gem_request *req)
 {
-	WARN_ON(!mutex_is_locked(&req->ring->dev->struct_mutex));
 	kref_put(&req->ref, i915_gem_request_free);
 }
 
-static inline void
-i915_gem_request_unreference__unlocked(struct drm_i915_gem_request *req)
-{
-	struct drm_device *dev;
-
-	if (!req)
-		return;
-
-	dev = req->ring->dev;
-	if (kref_put_mutex(&req->ref, i915_gem_request_free, &dev->struct_mutex))
-		mutex_unlock(&dev->struct_mutex);
-}
-
 static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
 					   struct drm_i915_gem_request *src)
 {
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index 82e4d15b6c18..d916e1325bd4 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -324,7 +324,7 @@ static int intel_breadcrumbs_signaller(void *arg)
 		if (signal_complete(signal)) {
 			intel_engine_remove_wait(engine, &signal->wait);
 
-			i915_gem_request_unreference__unlocked(signal->request);
+			i915_gem_request_unreference(signal->request);
 
 			spin_lock(&engine->breadcrumbs.lock);
 			rb_erase(&signal->node, &engine->breadcrumbs.signals);
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3c3766eab5c4..031830e87f8f 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11367,7 +11367,7 @@ static void intel_mmio_flip_work_func(struct work_struct *work)
 		WARN_ON(__i915_wait_request(mmio_flip->req,
 					    false, NULL,
 					    &mmio_flip->i915->rps.mmioflips));
-		i915_gem_request_unreference__unlocked(mmio_flip->req);
+		i915_gem_request_unreference(mmio_flip->req);
 	}
 
 	/* For framebuffer backed by dmabuf, wait for fence */
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index f543f897c516..f972078290b6 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -7196,7 +7196,7 @@ static void __intel_rps_boost_work(struct work_struct *work)
 		gen6_rps_boost(to_i915(req->ring->dev), NULL,
 			       req->emitted_jiffies);
 
-	i915_gem_request_unreference__unlocked(req);
+	i915_gem_request_unreference(req);
 	kfree(boost);
 }
 
-- 
2.6.3

_______________________________________________
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http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 3/3] drm/i915: Derive GEM requests from dma-fence

[Chris Wilson]

dma-buf provides a generic fence class for interoperation between
drivers. Internally we use the request structure as a fence, and so with
only a little bit of interfacing we can rebase those requests on top of
dma-buf fences. This will allow us, in the future, to pass those fences
back to userspace or between drivers.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/i915/i915_debugfs.c        |   2 +-
 drivers/gpu/drm/i915/i915_gem.c            |   2 +-
 drivers/gpu/drm/i915/i915_gem_request.c    | 128 ++++++++++++++++++++++++++---
 drivers/gpu/drm/i915/i915_gem_request.h    |  25 ++----
 drivers/gpu/drm/i915/i915_gpu_error.c      |   2 +-
 drivers/gpu/drm/i915/i915_guc_submission.c |   2 +-
 drivers/gpu/drm/i915/intel_breadcrumbs.c   |   3 +-
 drivers/gpu/drm/i915/intel_lrc.c           |   2 +-
 drivers/gpu/drm/i915/intel_ringbuffer.c    |  14 ++--
 9 files changed, 140 insertions(+), 40 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index 95fa6f7c8e00..d182c299d521 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -710,7 +710,7 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
 			if (req->pid)
 				task = pid_task(req->pid, PIDTYPE_PID);
 			seq_printf(m, "    %x @ %d: %s [%d]\n",
-				   req->seqno,
+				   req->fence.seqno,
 				   (int) (jiffies - req->emitted_jiffies),
 				   task ? task->comm : "<unknown>",
 				   task ? task->pid : -1);
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d92950b56f2d..8efc04547e23 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2264,7 +2264,7 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 
 	request->emitted_jiffies = jiffies;
 	request->previous_seqno = ring->last_submitted_seqno;
-	ring->last_submitted_seqno = request->seqno;
+	ring->last_submitted_seqno = request->fence.seqno;
 	list_add_tail(&request->list, &ring->request_list);
 
 	trace_i915_gem_request_add(request);
diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index bb88146dd90c..eec6b920e646 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -24,6 +24,115 @@
 
 #include "i915_drv.h"
 
+static inline struct drm_i915_gem_request *
+to_i915_request(struct fence *fence)
+{
+	return container_of(fence, struct drm_i915_gem_request, fence);
+}
+
+static const char *i915_fence_get_driver_name(struct fence *fence)
+{
+	return "i915";
+}
+
+static const char *i915_fence_get_timeline_name(struct fence *fence)
+{
+	return to_i915_request(fence)->ring->name;
+}
+
+static bool i915_fence_signaled(struct fence *fence)
+{
+	struct drm_i915_gem_request *request = to_i915_request(fence);
+
+	if (i915_gem_request_completed(request))
+		return true;
+
+	if (request->reset_counter != i915_reset_counter(&request->i915->gpu_error))
+		return true;
+
+	return false;
+}
+
+static bool i915_fence_enable_signaling(struct fence *fence)
+{
+	if (i915_fence_signaled(fence))
+		return false;
+
+	return intel_engine_add_signal(to_i915_request(fence)) == 0;
+}
+
+#define NO_WAITBOOST NULL /* FIXME! */
+
+static signed long i915_fence_wait(struct fence *fence,
+				   bool interruptible,
+				   signed long timeout_jiffies)
+{
+	s64 timeout_ns, *timeout;
+	int ret;
+
+	if (timeout_jiffies != MAX_SCHEDULE_TIMEOUT) {
+		timeout_ns = jiffies_to_nsecs(timeout_jiffies);
+		timeout = &timeout_ns;
+	} else
+		timeout = NULL;
+
+	ret = __i915_wait_request(to_i915_request(fence),
+				  interruptible, timeout,
+				  NO_WAITBOOST);
+	if (ret == -ETIME)
+		return 0;
+
+	if (ret < 0)
+		return ret;
+
+	if (timeout_jiffies != MAX_SCHEDULE_TIMEOUT)
+		timeout_jiffies = nsecs_to_jiffies(timeout_ns);
+
+	return timeout_jiffies;
+}
+
+static int i915_fence_fill_driver_data(struct fence *fence, void *data,
+				      int size)
+{
+	struct drm_i915_gem_request *request = to_i915_request(fence);
+
+	if (size < sizeof(request->fence.seqno))
+		return -ENOMEM;
+
+	memcpy(data, &request->fence.seqno, sizeof(request->fence.seqno));
+	return sizeof(request->fence.seqno);
+}
+
+static void i915_fence_value_str(struct fence *fence, char *str, int size)
+{
+	snprintf(str, size, "%u", fence->seqno);
+}
+
+static void i915_fence_timeline_value_str(struct fence *fence, char *str,
+					  int size)
+{
+	snprintf(str, size, "%u",
+		 intel_ring_get_seqno(to_i915_request(fence)->ring));
+}
+
+static void i915_fence_release(struct fence *fence)
+{
+	struct drm_i915_gem_request *req = to_i915_request(fence);
+	kmem_cache_free(req->i915->requests, req);
+}
+
+static const struct fence_ops i915_fence_ops = {
+	.get_driver_name = i915_fence_get_driver_name,
+	.get_timeline_name = i915_fence_get_timeline_name,
+	.enable_signaling = i915_fence_enable_signaling,
+	.signaled = i915_fence_signaled,
+	.wait = i915_fence_wait,
+	.release = i915_fence_release,
+	.fill_driver_data = i915_fence_fill_driver_data,
+	.fence_value_str = i915_fence_value_str,
+	.timeline_value_str = i915_fence_timeline_value_str,
+};
+
 static int
 i915_gem_check_wedge(unsigned reset_counter, bool interruptible)
 {
@@ -49,6 +158,7 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 	struct drm_i915_private *dev_priv = to_i915(ring->dev);
 	unsigned reset_counter = i915_reset_counter(&dev_priv->gpu_error);
 	struct drm_i915_gem_request *req;
+	u32 seqno;
 	int ret;
 
 	if (!req_out)
@@ -68,11 +178,13 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 	if (req == NULL)
 		return -ENOMEM;
 
-	ret = i915_gem_get_seqno(ring->dev, &req->seqno);
+	ret = i915_gem_get_seqno(ring->dev, &seqno);
 	if (ret)
 		goto err;
 
-	kref_init(&req->ref);
+	spin_lock_init(&req->lock);
+	fence_init(&req->fence, &i915_fence_ops, &req->lock, ring->id, seqno);
+
 	INIT_LIST_HEAD(&req->list);
 	req->i915 = dev_priv;
 	req->ring = ring;
@@ -362,7 +474,7 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	if (INTEL_INFO(req->i915)->gen >= 6)
 		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
-	intel_wait_init(&wait, req->seqno);
+	intel_wait_init(&wait, req->fence.seqno);
 	set_task_state(wait.task, state);
 
 	/* Optimistic spin for the next ~jiffie before touching IRQs */
@@ -453,7 +565,8 @@ out:
 			*timeout = 0;
 	}
 
-	if (ret == 0 && rps && req->seqno == req->ring->last_submitted_seqno) {
+	if (ret == 0 && rps &&
+	    req->fence.seqno == req->ring->last_submitted_seqno) {
 		/* The GPU is now idle and this client has stalled.
 		 * Since no other client has submitted a request in the
 		 * meantime, assume that this client is the only one
@@ -500,10 +613,3 @@ i915_wait_request(struct drm_i915_gem_request *req)
 	i915_gem_request_retire__upto(req);
 	return 0;
 }
-
-void i915_gem_request_free(struct kref *req_ref)
-{
-	struct drm_i915_gem_request *req =
-		container_of(req_ref, typeof(*req), ref);
-	kmem_cache_free(req->i915->requests, req);
-}
diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
index b19160a1511a..4198cd97e642 100644
--- a/drivers/gpu/drm/i915/i915_gem_request.h
+++ b/drivers/gpu/drm/i915/i915_gem_request.h
@@ -25,6 +25,8 @@
 #ifndef I915_GEM_REQUEST_H
 #define I915_GEM_REQUEST_H
 
+#include <linux/fence.h>
+
 /**
  * Request queue structure.
  *
@@ -36,11 +38,11 @@
  * emission time to be associated with the request for tracking how far ahead
  * of the GPU the submission is.
  *
- * The requests are reference counted, so upon creation they should have an
- * initial reference taken using kref_init
+ * The requests are reference counted.
  */
 struct drm_i915_gem_request {
-	struct kref ref;
+	struct fence fence;
+	spinlock_t lock;
 
 	/** On Which ring this request was generated */
 	struct drm_i915_private *i915;
@@ -53,12 +55,6 @@ struct drm_i915_gem_request {
 	  */
 	u32 previous_seqno;
 
-	 /** GEM sequence number associated with this request,
-	  * when the HWS breadcrumb is equal or greater than this the GPU
-	  * has finished processing this request.
-	  */
-	u32 seqno;
-
 	/** Position in the ringbuffer of the start of the request */
 	u32 head;
 
@@ -127,7 +123,6 @@ int i915_gem_request_alloc(struct intel_engine_cs *ring,
 			   struct intel_context *ctx,
 			   struct drm_i915_gem_request **req_out);
 void i915_gem_request_cancel(struct drm_i915_gem_request *req);
-void i915_gem_request_free(struct kref *req_ref);
 int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
 				   struct drm_file *file);
 void i915_gem_request_retire__upto(struct drm_i915_gem_request *req);
@@ -135,7 +130,7 @@ void i915_gem_request_retire__upto(struct drm_i915_gem_request *req);
 static inline uint32_t
 i915_gem_request_get_seqno(struct drm_i915_gem_request *req)
 {
-	return req ? req->seqno : 0;
+	return req ? req->fence.seqno : 0;
 }
 
 static inline struct intel_engine_cs *
@@ -147,15 +142,13 @@ i915_gem_request_get_ring(struct drm_i915_gem_request *req)
 static inline struct drm_i915_gem_request *
 i915_gem_request_reference(struct drm_i915_gem_request *req)
 {
-	if (req)
-		kref_get(&req->ref);
-	return req;
+	return container_of(fence_get(&req->fence), typeof(*req), fence);
 }
 
 static inline void
 i915_gem_request_unreference(struct drm_i915_gem_request *req)
 {
-	kref_put(&req->ref, i915_gem_request_free);
+	fence_put(&req->fence);
 }
 
 static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
@@ -188,7 +181,7 @@ static inline bool i915_gem_request_started(struct drm_i915_gem_request *req)
 static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req)
 {
 	return i915_seqno_passed(intel_ring_get_seqno(req->ring),
-				 req->seqno);
+				 req->fence.seqno);
 }
 
 
diff --git a/drivers/gpu/drm/i915/i915_gpu_error.c b/drivers/gpu/drm/i915/i915_gpu_error.c
index 6db6d7e02aea..70ac9badb950 100644
--- a/drivers/gpu/drm/i915/i915_gpu_error.c
+++ b/drivers/gpu/drm/i915/i915_gpu_error.c
@@ -1094,7 +1094,7 @@ static void i915_gem_record_rings(struct drm_device *dev,
 			}
 
 			erq = &error->ring[i].requests[count++];
-			erq->seqno = request->seqno;
+			erq->seqno = request->fence.seqno;
 			erq->jiffies = request->emitted_jiffies;
 			erq->tail = request->postfix;
 		}
diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 0d23785ba818..398c7c8c2815 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -609,7 +609,7 @@ int i915_guc_submit(struct i915_guc_client *client,
 		client->retcode = 0;
 	}
 	guc->submissions[ring_id] += 1;
-	guc->last_seqno[ring_id] = rq->seqno;
+	guc->last_seqno[ring_id] = rq->fence.seqno;
 
 	return q_ret;
 }
diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index d916e1325bd4..fa58a3f3b8bc 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -324,6 +324,7 @@ static int intel_breadcrumbs_signaller(void *arg)
 		if (signal_complete(signal)) {
 			intel_engine_remove_wait(engine, &signal->wait);
 
+			fence_signal(&signal->request->fence);
 			i915_gem_request_unreference(signal->request);
 
 			spin_lock(&engine->breadcrumbs.lock);
@@ -372,7 +373,7 @@ int intel_engine_add_signal(struct drm_i915_gem_request *request)
 	}
 
 	signal->wait.task = task;
-	signal->wait.seqno = request->seqno;
+	signal->wait.seqno = request->fence.seqno;
 
 	signal->request = i915_gem_request_reference(request);
 
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 009ab1321205..40645479dadd 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1768,7 +1768,7 @@ static int gen8_emit_request(struct drm_i915_gem_request *request)
 				(ring->status_page.gfx_addr +
 				(I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT)));
 	intel_logical_ring_emit(ringbuf, 0);
-	intel_logical_ring_emit(ringbuf, request->seqno);
+	intel_logical_ring_emit(ringbuf, request->fence.seqno);
 	intel_logical_ring_emit(ringbuf, MI_USER_INTERRUPT);
 	intel_logical_ring_emit(ringbuf, MI_NOOP);
 	intel_logical_ring_advance_and_submit(request);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 8ed1cac3a4f2..f68319a8a4cd 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1218,7 +1218,7 @@ static int gen8_rcs_signal(struct drm_i915_gem_request *signaller_req,
 					   PIPE_CONTROL_FLUSH_ENABLE);
 		intel_ring_emit(signaller, lower_32_bits(gtt_offset));
 		intel_ring_emit(signaller, upper_32_bits(gtt_offset));
-		intel_ring_emit(signaller, signaller_req->seqno);
+		intel_ring_emit(signaller, signaller_req->fence.seqno);
 		intel_ring_emit(signaller, 0);
 		intel_ring_emit(signaller, MI_SEMAPHORE_SIGNAL |
 					   MI_SEMAPHORE_TARGET(waiter->id));
@@ -1256,7 +1256,7 @@ static int gen8_xcs_signal(struct drm_i915_gem_request *signaller_req,
 		intel_ring_emit(signaller, lower_32_bits(gtt_offset) |
 					   MI_FLUSH_DW_USE_GTT);
 		intel_ring_emit(signaller, upper_32_bits(gtt_offset));
-		intel_ring_emit(signaller, signaller_req->seqno);
+		intel_ring_emit(signaller, signaller_req->fence.seqno);
 		intel_ring_emit(signaller, MI_SEMAPHORE_SIGNAL |
 					   MI_SEMAPHORE_TARGET(waiter->id));
 		intel_ring_emit(signaller, 0);
@@ -1289,7 +1289,7 @@ static int gen6_signal(struct drm_i915_gem_request *signaller_req,
 		if (i915_mmio_reg_valid(mbox_reg)) {
 			intel_ring_emit(signaller, MI_LOAD_REGISTER_IMM(1));
 			intel_ring_emit_reg(signaller, mbox_reg);
-			intel_ring_emit(signaller, signaller_req->seqno);
+			intel_ring_emit(signaller, signaller_req->fence.seqno);
 		}
 	}
 
@@ -1324,7 +1324,7 @@ gen6_add_request(struct drm_i915_gem_request *req)
 
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-	intel_ring_emit(ring, req->seqno);
+	intel_ring_emit(ring, req->fence.seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
 	__intel_ring_advance(ring);
 
@@ -1448,7 +1448,7 @@ pc_render_add_request(struct drm_i915_gem_request *req)
 			PIPE_CONTROL_QW_WRITE |
 			PIPE_CONTROL_WRITE_FLUSH);
 	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
-	intel_ring_emit(ring, req->seqno);
+	intel_ring_emit(ring, req->fence.seqno);
 	intel_ring_emit(ring, 0);
 	PIPE_CONTROL_FLUSH(ring, scratch_addr);
 	scratch_addr += 2 * CACHELINE_BYTES; /* write to separate cachelines */
@@ -1467,7 +1467,7 @@ pc_render_add_request(struct drm_i915_gem_request *req)
 			PIPE_CONTROL_WRITE_FLUSH |
 			PIPE_CONTROL_NOTIFY);
 	intel_ring_emit(ring, addr | PIPE_CONTROL_GLOBAL_GTT);
-	intel_ring_emit(ring, req->seqno);
+	intel_ring_emit(ring, req->fence.seqno);
 	intel_ring_emit(ring, 0);
 	__intel_ring_advance(ring);
 
@@ -1577,7 +1577,7 @@ i9xx_add_request(struct drm_i915_gem_request *req)
 
 	intel_ring_emit(ring, MI_STORE_DWORD_INDEX);
 	intel_ring_emit(ring, I915_GEM_HWS_INDEX << MI_STORE_DWORD_INDEX_SHIFT);
-	intel_ring_emit(ring, req->seqno);
+	intel_ring_emit(ring, req->fence.seqno);
 	intel_ring_emit(ring, MI_USER_INTERRUPT);
 	__intel_ring_advance(ring);
 
-- 
2.6.3

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Re: [PATCH 3/3] drm/i915: Derive GEM requests from dma-fence

[Dave Gordon]

On 12/12/15 15:34, Chris Wilson wrote:
> dma-buf provides a generic fence class for interoperation between
> drivers. Internally we use the request structure as a fence, and so with
> only a little bit of interfacing we can rebase those requests on top of
> dma-buf fences. This will allow us, in the future, to pass those fences
> back to userspace or between drivers.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c        |   2 +-
>   drivers/gpu/drm/i915/i915_gem.c            |   2 +-
>   drivers/gpu/drm/i915/i915_gem_request.c    | 128 ++++++++++++++++++++++++++---
>   drivers/gpu/drm/i915/i915_gem_request.h    |  25 ++----
>   drivers/gpu/drm/i915/i915_gpu_error.c      |   2 +-
>   drivers/gpu/drm/i915/i915_guc_submission.c |   2 +-
>   drivers/gpu/drm/i915/intel_breadcrumbs.c   |   3 +-
>   drivers/gpu/drm/i915/intel_lrc.c           |   2 +-
>   drivers/gpu/drm/i915/intel_ringbuffer.c    |  14 ++--
>   9 files changed, 140 insertions(+), 40 deletions(-)

This seems to be doing the same thing as John Harrison's patch

[PATCH 05/13] drm/i915: Convert requests to use struct fence

Likewise you both have a patch to remove lazy coherency, and various 
other duplications:

[PATCH 06/13] drm/i915: Removed now redudant parameter to 
i915_gem_request_completed()
[PATCH 08/13] drm/i915: Delay the freeing of requests until retire time

These will have to be unified; we just have to pick exactly how to make 
each of these improvements.

.Dave.
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Re: [PATCH 3/3] drm/i915: Derive GEM requests from dma-fence

[Chris Wilson]

On Mon, Jan 04, 2016 at 12:17:47PM +0000, Dave Gordon wrote:
> On 12/12/15 15:34, Chris Wilson wrote:
> >dma-buf provides a generic fence class for interoperation between
> >drivers. Internally we use the request structure as a fence, and so with
> >only a little bit of interfacing we can rebase those requests on top of
> >dma-buf fences. This will allow us, in the future, to pass those fences
> >back to userspace or between drivers.
> >
> >Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> >Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
> >Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >---
> >  drivers/gpu/drm/i915/i915_debugfs.c        |   2 +-
> >  drivers/gpu/drm/i915/i915_gem.c            |   2 +-
> >  drivers/gpu/drm/i915/i915_gem_request.c    | 128 ++++++++++++++++++++++++++---
> >  drivers/gpu/drm/i915/i915_gem_request.h    |  25 ++----
> >  drivers/gpu/drm/i915/i915_gpu_error.c      |   2 +-
> >  drivers/gpu/drm/i915/i915_guc_submission.c |   2 +-
> >  drivers/gpu/drm/i915/intel_breadcrumbs.c   |   3 +-
> >  drivers/gpu/drm/i915/intel_lrc.c           |   2 +-
> >  drivers/gpu/drm/i915/intel_ringbuffer.c    |  14 ++--
> >  9 files changed, 140 insertions(+), 40 deletions(-)
> 
> This seems to be doing the same thing as John Harrison's patch
> 
> [PATCH 05/13] drm/i915: Convert requests to use struct fence
> 
> Likewise you both have a patch to remove lazy coherency, and various
> other duplications:
> 
> [PATCH 06/13] drm/i915: Removed now redudant parameter to
> i915_gem_request_completed()
> [PATCH 08/13] drm/i915: Delay the freeing of requests until retire time
> 
> These will have to be unified; we just have to pick exactly how to
> make each of these improvements.

Indeed. This is my rebuttal of those patches since they did not
understand the issues involved.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/intel-gfx

[PATCH 26/32] drm/i915: Move the get/put irq locking into the caller

[Chris Wilson]

With only a single callsite for intel_engine_cs->irq_get and ->irq_put,
we can reduce the code size by moving the common preamble into the
caller, and we can also eliminate the reference counting.

For completeness, as we are no longer doing reference counting on irq,
rename the get/put vfunctions to enable/disable respectively.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/intel_breadcrumbs.c |   8 +-
 drivers/gpu/drm/i915/intel_lrc.c         |  53 ++----
 drivers/gpu/drm/i915/intel_ringbuffer.c  | 302 ++++++++++---------------------
 drivers/gpu/drm/i915/intel_ringbuffer.h  |   5 +-
 4 files changed, 125 insertions(+), 243 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index ea5ee3f7fe01..373e79fb2892 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -46,12 +46,16 @@ static void intel_breadcrumbs_fake_irq(unsigned long data)
 
 static void irq_enable(struct intel_engine_cs *engine)
 {
-	WARN_ON(!engine->irq_get(engine));
+	spin_lock_irq(&engine->i915->irq_lock);
+	engine->irq_enable(engine);
+	spin_unlock_irq(&engine->i915->irq_lock);
 }
 
 static void irq_disable(struct intel_engine_cs *engine)
 {
-	engine->irq_put(engine);
+	spin_lock_irq(&engine->i915->irq_lock);
+	engine->irq_disable(engine);
+	spin_unlock_irq(&engine->i915->irq_lock);
 }
 
 static void __intel_breadcrumbs_enable_irq(struct intel_breadcrumbs *b)
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index a73c5e671423..868271dfa7eb 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -1610,37 +1610,20 @@ static int gen8_emit_bb_start(struct drm_i915_gem_request *req,
 	return 0;
 }
 
-static bool gen8_logical_ring_get_irq(struct intel_engine_cs *ring)
+static void gen8_logical_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		I915_WRITE_IMR(ring, ~(ring->irq_enable_mask | ring->irq_keep_mask));
-		POSTING_READ(RING_IMR(ring->mmio_base));
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	return true;
+	I915_WRITE_IMR(ring, ~(ring->irq_enable_mask | ring->irq_keep_mask));
+	POSTING_READ(RING_IMR(ring->mmio_base));
 }
 
-static void gen8_logical_ring_put_irq(struct intel_engine_cs *ring)
+static void gen8_logical_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		I915_WRITE_IMR(ring, ~ring->irq_keep_mask);
-		POSTING_READ(RING_IMR(ring->mmio_base));
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	I915_WRITE_IMR(ring, ~ring->irq_keep_mask);
+	POSTING_READ(RING_IMR(ring->mmio_base));
 }
 
 static int gen8_emit_flush(struct drm_i915_gem_request *request,
@@ -1963,8 +1946,8 @@ static int logical_render_ring_init(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush_render;
-	ring->irq_get = gen8_logical_ring_get_irq;
-	ring->irq_put = gen8_logical_ring_put_irq;
+	ring->irq_enable = gen8_logical_ring_enable_irq;
+	ring->irq_disable = gen8_logical_ring_disable_irq;
 	ring->emit_bb_start = gen8_emit_bb_start;
 
 	ring->dev = dev;
@@ -2009,8 +1992,8 @@ static int logical_bsd_ring_init(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
-	ring->irq_get = gen8_logical_ring_get_irq;
-	ring->irq_put = gen8_logical_ring_put_irq;
+	ring->irq_enable = gen8_logical_ring_enable_irq;
+	ring->irq_disable = gen8_logical_ring_disable_irq;
 	ring->emit_bb_start = gen8_emit_bb_start;
 
 	return logical_ring_init(dev, ring);
@@ -2033,8 +2016,8 @@ static int logical_bsd2_ring_init(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
-	ring->irq_get = gen8_logical_ring_get_irq;
-	ring->irq_put = gen8_logical_ring_put_irq;
+	ring->irq_enable = gen8_logical_ring_enable_irq;
+	ring->irq_disable = gen8_logical_ring_disable_irq;
 	ring->emit_bb_start = gen8_emit_bb_start;
 
 	return logical_ring_init(dev, ring);
@@ -2057,8 +2040,8 @@ static int logical_blt_ring_init(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
-	ring->irq_get = gen8_logical_ring_get_irq;
-	ring->irq_put = gen8_logical_ring_put_irq;
+	ring->irq_enable = gen8_logical_ring_enable_irq;
+	ring->irq_disable = gen8_logical_ring_disable_irq;
 	ring->emit_bb_start = gen8_emit_bb_start;
 
 	return logical_ring_init(dev, ring);
@@ -2081,8 +2064,8 @@ static int logical_vebox_ring_init(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->emit_request = gen8_emit_request;
 	ring->emit_flush = gen8_emit_flush;
-	ring->irq_get = gen8_logical_ring_get_irq;
-	ring->irq_put = gen8_logical_ring_put_irq;
+	ring->irq_enable = gen8_logical_ring_enable_irq;
+	ring->irq_disable = gen8_logical_ring_disable_irq;
 	ring->emit_bb_start = gen8_emit_bb_start;
 
 	return logical_ring_init(dev, ring);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 14cd326ea99e..38af4b96f639 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -1503,109 +1503,56 @@ gen6_seqno_barrier(struct intel_engine_cs *ring)
 	intel_flush_status_page(ring, I915_GEM_HWS_INDEX);
 }
 
-static bool
-gen5_ring_get_irq(struct intel_engine_cs *ring)
+static void
+gen5_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0)
-		gen5_enable_gt_irq(dev_priv, ring->irq_enable_mask);
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
-
-	return true;
+	gen5_enable_gt_irq(ring->i915, ring->irq_enable_mask);
 }
 
 static void
-gen5_ring_put_irq(struct intel_engine_cs *ring)
+gen5_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0)
-		gen5_disable_gt_irq(dev_priv, ring->irq_enable_mask);
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	gen5_disable_gt_irq(ring->i915, ring->irq_enable_mask);
 }
 
-static bool
-i9xx_ring_get_irq(struct intel_engine_cs *ring)
+static void
+i9xx_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (!intel_irqs_enabled(dev_priv))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		dev_priv->irq_mask &= ~ring->irq_enable_mask;
-		I915_WRITE(IMR, dev_priv->irq_mask);
-		POSTING_READ(IMR);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	return true;
+	dev_priv->irq_mask &= ~ring->irq_enable_mask;
+	I915_WRITE(IMR, dev_priv->irq_mask);
+	POSTING_READ(IMR);
 }
 
 static void
-i9xx_ring_put_irq(struct intel_engine_cs *ring)
+i9xx_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		dev_priv->irq_mask |= ring->irq_enable_mask;
-		I915_WRITE(IMR, dev_priv->irq_mask);
-		POSTING_READ(IMR);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	dev_priv->irq_mask |= ring->irq_enable_mask;
+	I915_WRITE(IMR, dev_priv->irq_mask);
+	POSTING_READ(IMR);
 }
 
-static bool
-i8xx_ring_get_irq(struct intel_engine_cs *ring)
+static void
+i8xx_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (!intel_irqs_enabled(dev_priv))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		dev_priv->irq_mask &= ~ring->irq_enable_mask;
-		I915_WRITE16(IMR, dev_priv->irq_mask);
-		POSTING_READ16(IMR);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	return true;
+	dev_priv->irq_mask &= ~ring->irq_enable_mask;
+	I915_WRITE16(IMR, dev_priv->irq_mask);
+	POSTING_READ16(IMR);
 }
 
 static void
-i8xx_ring_put_irq(struct intel_engine_cs *ring)
+i8xx_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		dev_priv->irq_mask |= ring->irq_enable_mask;
-		I915_WRITE16(IMR, dev_priv->irq_mask);
-		POSTING_READ16(IMR);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	dev_priv->irq_mask |= ring->irq_enable_mask;
+	I915_WRITE16(IMR, dev_priv->irq_mask);
+	POSTING_READ16(IMR);
 }
 
 static int
@@ -1645,128 +1592,77 @@ i9xx_add_request(struct drm_i915_gem_request *req)
 	return 0;
 }
 
-static bool
-gen6_ring_get_irq(struct intel_engine_cs *ring)
+static void
+gen6_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		if (HAS_L3_DPF(dev) && ring->id == RCS)
-			I915_WRITE_IMR(ring,
-				       ~(ring->irq_enable_mask |
-					 GT_PARITY_ERROR(dev)));
-		else
-			I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
-		gen5_enable_gt_irq(dev_priv, ring->irq_enable_mask);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	return true;
+	if (HAS_L3_DPF(dev_priv) && ring->id == RCS)
+		I915_WRITE_IMR(ring,
+			       ~(ring->irq_enable_mask |
+				 GT_PARITY_ERROR(dev_priv)));
+	else
+		I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
+	gen5_enable_gt_irq(dev_priv, ring->irq_enable_mask);
 }
 
 static void
-gen6_ring_put_irq(struct intel_engine_cs *ring)
+gen6_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		if (HAS_L3_DPF(dev) && ring->id == RCS)
-			I915_WRITE_IMR(ring, ~GT_PARITY_ERROR(dev));
-		else
-			I915_WRITE_IMR(ring, ~0);
-		gen5_disable_gt_irq(dev_priv, ring->irq_enable_mask);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	if (HAS_L3_DPF(dev_priv) && ring->id == RCS)
+		I915_WRITE_IMR(ring, ~GT_PARITY_ERROR(dev_priv));
+	else
+		I915_WRITE_IMR(ring, ~0);
+	gen5_disable_gt_irq(dev_priv, ring->irq_enable_mask);
 }
 
-static bool
-hsw_vebox_get_irq(struct intel_engine_cs *ring)
+static void
+hsw_vebox_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return false;
-
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
-		gen6_enable_pm_irq(dev_priv, ring->irq_enable_mask);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	return true;
+	I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
+	gen6_enable_pm_irq(dev_priv, ring->irq_enable_mask);
 }
 
 static void
-hsw_vebox_put_irq(struct intel_engine_cs *ring)
+hsw_vebox_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		I915_WRITE_IMR(ring, ~0);
-		gen6_disable_pm_irq(dev_priv, ring->irq_enable_mask);
-	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	I915_WRITE_IMR(ring, ~0);
+	gen6_disable_pm_irq(dev_priv, ring->irq_enable_mask);
 }
 
-static bool
-gen8_ring_get_irq(struct intel_engine_cs *ring)
+static void
+gen8_ring_enable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
-
-	if (WARN_ON(!intel_irqs_enabled(dev_priv)))
-		return false;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (ring->irq_refcount++ == 0) {
-		if (HAS_L3_DPF(dev) && ring->id == RCS) {
-			I915_WRITE_IMR(ring,
-				       ~(ring->irq_enable_mask |
-					 GT_RENDER_L3_PARITY_ERROR_INTERRUPT));
-		} else {
-			I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
-		}
-		POSTING_READ(RING_IMR(ring->mmio_base));
+	if (HAS_L3_DPF(dev_priv) && ring->id == RCS) {
+		I915_WRITE_IMR(ring,
+			       ~(ring->irq_enable_mask |
+				 GT_RENDER_L3_PARITY_ERROR_INTERRUPT));
+	} else {
+		I915_WRITE_IMR(ring, ~ring->irq_enable_mask);
 	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
-
-	return true;
+	POSTING_READ(RING_IMR(ring->mmio_base));
 }
 
 static void
-gen8_ring_put_irq(struct intel_engine_cs *ring)
+gen8_ring_disable_irq(struct intel_engine_cs *ring)
 {
-	struct drm_device *dev = ring->dev;
-	struct drm_i915_private *dev_priv = dev->dev_private;
-	unsigned long flags;
+	struct drm_i915_private *dev_priv = ring->i915;
 
-	spin_lock_irqsave(&dev_priv->irq_lock, flags);
-	if (--ring->irq_refcount == 0) {
-		if (HAS_L3_DPF(dev) && ring->id == RCS) {
-			I915_WRITE_IMR(ring,
-				       ~GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
-		} else {
-			I915_WRITE_IMR(ring, ~0);
-		}
-		POSTING_READ(RING_IMR(ring->mmio_base));
+	if (HAS_L3_DPF(dev_priv) && ring->id == RCS) {
+		I915_WRITE_IMR(ring,
+			       ~GT_RENDER_L3_PARITY_ERROR_INTERRUPT);
+	} else {
+		I915_WRITE_IMR(ring, ~0);
 	}
-	spin_unlock_irqrestore(&dev_priv->irq_lock, flags);
+	POSTING_READ(RING_IMR(ring->mmio_base));
 }
 
 static int
@@ -2667,8 +2563,8 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->init_context = intel_rcs_ctx_init;
 		ring->add_request = gen6_add_request;
 		ring->flush = gen8_render_ring_flush;
-		ring->irq_get = gen8_ring_get_irq;
-		ring->irq_put = gen8_ring_put_irq;
+		ring->irq_enable = gen8_ring_enable_irq;
+		ring->irq_disable = gen8_ring_disable_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
 		ring->seqno_barrier = gen6_seqno_barrier;
 		if (i915_semaphore_is_enabled(dev)) {
@@ -2683,8 +2579,8 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		ring->flush = gen7_render_ring_flush;
 		if (INTEL_INFO(dev)->gen == 6)
 			ring->flush = gen6_render_ring_flush;
-		ring->irq_get = gen6_ring_get_irq;
-		ring->irq_put = gen6_ring_put_irq;
+		ring->irq_enable = gen6_ring_enable_irq;
+		ring->irq_disable = gen6_ring_disable_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT;
 		ring->seqno_barrier = gen6_seqno_barrier;
 		if (i915_semaphore_is_enabled(dev)) {
@@ -2711,8 +2607,8 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 	} else if (IS_GEN5(dev)) {
 		ring->add_request = pc_render_add_request;
 		ring->flush = gen4_render_ring_flush;
-		ring->irq_get = gen5_ring_get_irq;
-		ring->irq_put = gen5_ring_put_irq;
+		ring->irq_enable = gen5_ring_enable_irq;
+		ring->irq_disable = gen5_ring_disable_irq;
 		ring->irq_enable_mask = GT_RENDER_USER_INTERRUPT |
 					GT_RENDER_PIPECTL_NOTIFY_INTERRUPT;
 	} else {
@@ -2722,11 +2618,11 @@ int intel_init_render_ring_buffer(struct drm_device *dev)
 		else
 			ring->flush = gen4_render_ring_flush;
 		if (IS_GEN2(dev)) {
-			ring->irq_get = i8xx_ring_get_irq;
-			ring->irq_put = i8xx_ring_put_irq;
+			ring->irq_enable = i8xx_ring_enable_irq;
+			ring->irq_disable = i8xx_ring_disable_irq;
 		} else {
-			ring->irq_get = i9xx_ring_get_irq;
-			ring->irq_put = i9xx_ring_put_irq;
+			ring->irq_enable = i9xx_ring_enable_irq;
+			ring->irq_disable = i9xx_ring_disable_irq;
 		}
 		ring->irq_enable_mask = I915_USER_INTERRUPT;
 	}
@@ -2799,8 +2695,8 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 		if (INTEL_INFO(dev)->gen >= 8) {
 			ring->irq_enable_mask =
 				GT_RENDER_USER_INTERRUPT << GEN8_VCS1_IRQ_SHIFT;
-			ring->irq_get = gen8_ring_get_irq;
-			ring->irq_put = gen8_ring_put_irq;
+			ring->irq_enable = gen8_ring_enable_irq;
+			ring->irq_disable = gen8_ring_disable_irq;
 			ring->dispatch_execbuffer =
 				gen8_ring_dispatch_execbuffer;
 			if (i915_semaphore_is_enabled(dev)) {
@@ -2810,8 +2706,8 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 			}
 		} else {
 			ring->irq_enable_mask = GT_BSD_USER_INTERRUPT;
-			ring->irq_get = gen6_ring_get_irq;
-			ring->irq_put = gen6_ring_put_irq;
+			ring->irq_enable = gen6_ring_enable_irq;
+			ring->irq_disable = gen6_ring_disable_irq;
 			ring->dispatch_execbuffer =
 				gen6_ring_dispatch_execbuffer;
 			if (i915_semaphore_is_enabled(dev)) {
@@ -2835,12 +2731,12 @@ int intel_init_bsd_ring_buffer(struct drm_device *dev)
 		ring->add_request = i9xx_add_request;
 		if (IS_GEN5(dev)) {
 			ring->irq_enable_mask = ILK_BSD_USER_INTERRUPT;
-			ring->irq_get = gen5_ring_get_irq;
-			ring->irq_put = gen5_ring_put_irq;
+			ring->irq_enable = gen5_ring_enable_irq;
+			ring->irq_disable = gen5_ring_disable_irq;
 		} else {
 			ring->irq_enable_mask = I915_BSD_USER_INTERRUPT;
-			ring->irq_get = i9xx_ring_get_irq;
-			ring->irq_put = i9xx_ring_put_irq;
+			ring->irq_enable = i9xx_ring_enable_irq;
+			ring->irq_disable = i9xx_ring_disable_irq;
 		}
 		ring->dispatch_execbuffer = i965_dispatch_execbuffer;
 	}
@@ -2867,8 +2763,8 @@ int intel_init_bsd2_ring_buffer(struct drm_device *dev)
 	ring->seqno_barrier = gen6_seqno_barrier;
 	ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_VCS2_IRQ_SHIFT;
-	ring->irq_get = gen8_ring_get_irq;
-	ring->irq_put = gen8_ring_put_irq;
+	ring->irq_enable = gen8_ring_enable_irq;
+	ring->irq_disable = gen8_ring_disable_irq;
 	ring->dispatch_execbuffer =
 			gen8_ring_dispatch_execbuffer;
 	if (i915_semaphore_is_enabled(dev)) {
@@ -2897,8 +2793,8 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
 	if (INTEL_INFO(dev)->gen >= 8) {
 		ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_BCS_IRQ_SHIFT;
-		ring->irq_get = gen8_ring_get_irq;
-		ring->irq_put = gen8_ring_put_irq;
+		ring->irq_enable = gen8_ring_enable_irq;
+		ring->irq_disable = gen8_ring_disable_irq;
 		ring->dispatch_execbuffer = gen8_ring_dispatch_execbuffer;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.sync_to = gen8_ring_sync;
@@ -2907,8 +2803,8 @@ int intel_init_blt_ring_buffer(struct drm_device *dev)
 		}
 	} else {
 		ring->irq_enable_mask = GT_BLT_USER_INTERRUPT;
-		ring->irq_get = gen6_ring_get_irq;
-		ring->irq_put = gen6_ring_put_irq;
+		ring->irq_enable = gen6_ring_enable_irq;
+		ring->irq_disable = gen6_ring_disable_irq;
 		ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.signal = gen6_signal;
@@ -2954,8 +2850,8 @@ int intel_init_vebox_ring_buffer(struct drm_device *dev)
 	if (INTEL_INFO(dev)->gen >= 8) {
 		ring->irq_enable_mask =
 			GT_RENDER_USER_INTERRUPT << GEN8_VECS_IRQ_SHIFT;
-		ring->irq_get = gen8_ring_get_irq;
-		ring->irq_put = gen8_ring_put_irq;
+		ring->irq_enable = gen8_ring_enable_irq;
+		ring->irq_disable = gen8_ring_disable_irq;
 		ring->dispatch_execbuffer = gen8_ring_dispatch_execbuffer;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.sync_to = gen8_ring_sync;
@@ -2964,8 +2860,8 @@ int intel_init_vebox_ring_buffer(struct drm_device *dev)
 		}
 	} else {
 		ring->irq_enable_mask = PM_VEBOX_USER_INTERRUPT;
-		ring->irq_get = hsw_vebox_get_irq;
-		ring->irq_put = hsw_vebox_put_irq;
+		ring->irq_enable = hsw_vebox_enable_irq;
+		ring->irq_disable = hsw_vebox_disable_irq;
 		ring->dispatch_execbuffer = gen6_ring_dispatch_execbuffer;
 		if (i915_semaphore_is_enabled(dev)) {
 			ring->semaphore.sync_to = gen6_ring_sync;
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 0fd6395f1a1b..33780fad6a30 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -198,10 +198,9 @@ struct  intel_engine_cs {
 	struct intel_hw_status_page status_page;
 	struct i915_ctx_workarounds wa_ctx;
 
-	unsigned irq_refcount; /* protected by dev_priv->irq_lock */
 	u32		irq_enable_mask;	/* bitmask to enable ring interrupt */
-	bool __must_check (*irq_get)(struct intel_engine_cs *ring);
-	void		(*irq_put)(struct intel_engine_cs *ring);
+	void		(*irq_enable)(struct intel_engine_cs *ring);
+	void		(*irq_disable)(struct intel_engine_cs *ring);
 
 	int		(*init_hw)(struct intel_engine_cs *ring);
 
-- 
2.6.3

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[PATCH 27/32] drm/i915: Harden detection of missed interrupts

[Chris Wilson]

Only declare a missed interrupt if we find that the GPU is idle with
waiters and a hangcheck interval has passed in which no new user
interrupts have been raised.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_debugfs.c     | 6 ++++++
 drivers/gpu/drm/i915/i915_irq.c         | 7 ++++++-
 drivers/gpu/drm/i915/intel_ringbuffer.h | 2 ++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index a03ed9e38499..78506abe7882 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -735,6 +735,9 @@ static void i915_ring_seqno_info(struct seq_file *m,
 	seq_printf(m, "Current sequence (%s): %x\n",
 		   ring->name, intel_ring_get_seqno(ring));
 
+	seq_printf(m, "Current user interrupts (%s): %x\n",
+		   ring->name, READ_ONCE(ring->user_interrupts));
+
 	spin_lock(&ring->breadcrumbs.lock);
 	for (rb = rb_first(&ring->breadcrumbs.requests);
 	     rb != NULL;
@@ -1369,6 +1372,9 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 		seq_printf(m, "\tseqno = %x [current %x], waiters? %d\n",
 			   ring->hangcheck.seqno, seqno[i],
 			   intel_engine_has_waiter(ring));
+		seq_printf(m, "\tuser interrupts = %x [current %x]\n",
+			   ring->hangcheck.user_interrupts,
+			   ring->user_interrupts);
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
 			   (long long)acthd[i]);
diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 64502c0d2a81..e864ebeef4ef 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1000,6 +1000,7 @@ static void notify_ring(struct intel_engine_cs *ring)
 		return;
 
 	trace_i915_gem_request_notify(ring);
+	ring->user_interrupts++;
 	intel_engine_wakeup(ring);
 }
 
@@ -2974,12 +2975,14 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 	for_each_ring(ring, dev_priv, i) {
 		u64 acthd;
 		u32 seqno;
+		unsigned user_interrupts;
 		bool busy = true;
 
 		semaphore_clear_deadlocks(dev_priv);
 
 		acthd = intel_ring_get_active_head(ring);
 		seqno = intel_ring_get_seqno(ring);
+		user_interrupts = ring->user_interrupts;
 
 		if (ring->hangcheck.seqno == seqno) {
 			if (ring_idle(ring, seqno)) {
@@ -2987,7 +2990,8 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 				if (intel_engine_has_waiter(ring)) {
 					/* Issue a wake-up to catch stuck h/w. */
-					if (!test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
+					if (ring->hangcheck.user_interrupts == user_interrupts &&
+					    !test_and_set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings)) {
 						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
@@ -3051,6 +3055,7 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 
 		ring->hangcheck.seqno = seqno;
 		ring->hangcheck.acthd = acthd;
+		ring->hangcheck.user_interrupts = user_interrupts;
 		busy_count += busy;
 	}
 
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index 33780fad6a30..1b4aa59c4d21 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -90,6 +90,7 @@ struct intel_ring_hangcheck {
 	u64 acthd;
 	u64 max_acthd;
 	u32 seqno;
+	unsigned user_interrupts;
 	int score;
 	enum intel_ring_hangcheck_action action;
 	int deadlock;
@@ -323,6 +324,7 @@ struct  intel_engine_cs {
 	 * inspecting request list.
 	 */
 	u32 last_submitted_seqno;
+	unsigned user_interrupts;
 
 	bool gpu_caches_dirty;
 
-- 
2.6.3

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[PATCH 28/32] drm/i915: Remove debug noise on detecting fault-injection of missed interrupts

[Chris Wilson]

Since the tests can and do explicitly check debugfs/i915_ring_missed_irqs
for the handling of a "missed interrupt", adding it to the dmesg at INFO
is just noise. When it happens for real, we still class it as an ERROR.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_irq.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index e864ebeef4ef..e5e307654c66 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2995,9 +2995,6 @@ static void i915_hangcheck_elapsed(struct work_struct *work)
 						if (!test_bit(ring->id, &dev_priv->gpu_error.test_irq_rings))
 							DRM_ERROR("Hangcheck timer elapsed... %s idle\n",
 								  ring->name);
-						else
-							DRM_INFO("Fake missed irq on %s\n",
-								 ring->name);
 
 						intel_engine_enable_fake_irq(ring);
 					}
-- 
2.6.3

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[PATCH 29/32] drm/i915: Only start retire worker when idle

[Chris Wilson]

The retire worker is a low frequency task that makes sure we retire
outstanding requests if userspace is being lax. We only need to start it
once as it remains active until the GPU is idle, so do a cheap test
before the more expensive queue_work(). A consequence of this is that we
need correct locking in the worker to make the hot path of request
submission cheap. To keep the symmetry and keep hangcheck strictly bound
by the GPU's wakelock, we move the cancel_sync(hangcheck) to the idle
worker before dropping the wakelock.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
References: https://bugs.freedesktop.org/show_bug.cgi?id=88437
---
 drivers/gpu/drm/i915/i915_drv.c      |  2 -
 drivers/gpu/drm/i915/i915_drv.h      |  2 +-
 drivers/gpu/drm/i915/i915_gem.c      | 97 +++++++++++++++++++++++++-----------
 drivers/gpu/drm/i915/intel_display.c | 29 -----------
 4 files changed, 69 insertions(+), 61 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index ba91f65b6082..0f79ee1d35a2 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1472,8 +1472,6 @@ static int intel_runtime_suspend(struct device *device)
 	i915_gem_release_all_mmaps(dev_priv);
 	mutex_unlock(&dev->struct_mutex);
 
-	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
-
 	intel_guc_suspend(dev);
 
 	intel_suspend_gt_powersave(dev);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index dabfb043362f..834cc779a9db 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2996,7 +2996,7 @@ int __must_check i915_gem_set_seqno(struct drm_device *dev, u32 seqno);
 struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *ring);
 
-bool i915_gem_retire_requests(struct drm_device *dev);
+void i915_gem_retire_requests(struct drm_device *dev);
 void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index fdd9dd5296e9..d1a7a7f8f3ad 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2495,6 +2495,51 @@ i915_gem_get_seqno(struct drm_device *dev, u32 *seqno)
 	return 0;
 }
 
+static void i915_gem_mark_busy(struct drm_i915_private *dev_priv)
+{
+	if (dev_priv->mm.busy)
+		return;
+
+	intel_runtime_pm_get_noresume(dev_priv);
+
+	i915_update_gfx_val(dev_priv);
+	if (INTEL_INFO(dev_priv)->gen >= 6)
+		gen6_rps_busy(dev_priv);
+
+	queue_delayed_work(dev_priv->wq,
+			   &dev_priv->mm.retire_work,
+			   round_jiffies_up_relative(HZ));
+
+	dev_priv->mm.busy = true;
+}
+
+static void kick_waiters(struct drm_i915_private *dev_priv)
+{
+	struct intel_engine_cs *ring;
+	int i;
+
+	for_each_ring(ring, dev_priv, i) {
+		if (!intel_engine_has_waiter(ring))
+			continue;
+
+		set_bit(ring->id, &dev_priv->gpu_error.missed_irq_rings);
+		intel_engine_wakeup(ring);
+	}
+}
+
+static void i915_gem_mark_idle(struct drm_i915_private *dev_priv)
+{
+	dev_priv->mm.busy = false;
+
+	if (cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work))
+		kick_waiters(dev_priv);
+
+	if (INTEL_INFO(dev_priv)->gen >= 6)
+		gen6_rps_idle(dev_priv);
+
+	intel_runtime_pm_put(dev_priv);
+}
+
 /*
  * NB: This function is not allowed to fail. Doing so would mean the the
  * request is not being tracked for completion but the work itself is
@@ -2575,10 +2620,7 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 
 	trace_i915_gem_request_add(request);
 
-	queue_delayed_work(dev_priv->wq,
-			   &dev_priv->mm.retire_work,
-			   round_jiffies_up_relative(HZ));
-	intel_mark_busy(dev_priv->dev);
+	i915_gem_mark_busy(dev_priv);
 
 	/* Sanity check that the reserved size was large enough. */
 	intel_ring_reserved_space_end(ringbuf);
@@ -2910,7 +2952,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 	WARN_ON(i915_verify_lists(ring->dev));
 }
 
-bool
+void
 i915_gem_retire_requests(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -2934,10 +2976,8 @@ i915_gem_retire_requests(struct drm_device *dev)
 
 	if (idle)
 		mod_delayed_work(dev_priv->wq,
-				   &dev_priv->mm.idle_work,
-				   msecs_to_jiffies(100));
-
-	return idle;
+				 &dev_priv->mm.idle_work,
+				 msecs_to_jiffies(100));
 }
 
 static void
@@ -2946,16 +2986,20 @@ i915_gem_retire_work_handler(struct work_struct *work)
 	struct drm_i915_private *dev_priv =
 		container_of(work, typeof(*dev_priv), mm.retire_work.work);
 	struct drm_device *dev = dev_priv->dev;
-	bool idle;
 
 	/* Come back later if the device is busy... */
-	idle = false;
 	if (mutex_trylock(&dev->struct_mutex)) {
-		idle = i915_gem_retire_requests(dev);
+		i915_gem_retire_requests(dev);
 		mutex_unlock(&dev->struct_mutex);
 	}
-	if (!idle)
-		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work,
+
+	/* Keep the retire handler running until we are finally idle.
+	 * We do not need to do this test under locking as in the worst-case
+	 * we queue the retire worker once too often.
+	 */
+	if (READ_ONCE(dev_priv->mm.busy))
+		queue_delayed_work(dev_priv->wq,
+				   &dev_priv->mm.retire_work,
 				   round_jiffies_up_relative(HZ));
 }
 
@@ -2968,25 +3012,20 @@ i915_gem_idle_work_handler(struct work_struct *work)
 	struct intel_engine_cs *ring;
 	int i;
 
-	for_each_ring(ring, dev_priv, i)
-		if (!list_empty(&ring->request_list))
-			return;
-
-	/* we probably should sync with hangcheck here, using cancel_work_sync.
-	 * Also locking seems to be fubar here, ring->request_list is protected
-	 * by dev->struct_mutex. */
+	if (!mutex_trylock(&dev->struct_mutex))
+		return;
 
-	intel_mark_idle(dev);
+	for_each_ring(ring, dev_priv, i) {
+		if (!list_empty(&ring->request_list))
+			goto out;
 
-	if (mutex_trylock(&dev->struct_mutex)) {
-		struct intel_engine_cs *ring;
-		int i;
+		i915_gem_batch_pool_fini(&ring->batch_pool);
+	}
 
-		for_each_ring(ring, dev_priv, i)
-			i915_gem_batch_pool_fini(&ring->batch_pool);
+	i915_gem_mark_idle(dev_priv);
 
-		mutex_unlock(&dev->struct_mutex);
-	}
+out:
+	mutex_unlock(&dev->struct_mutex);
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ffcdc2c631e1..3c3766eab5c4 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10810,35 +10810,6 @@ struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 	return mode;
 }
 
-void intel_mark_busy(struct drm_device *dev)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	if (dev_priv->mm.busy)
-		return;
-
-	intel_runtime_pm_get(dev_priv);
-	i915_update_gfx_val(dev_priv);
-	if (INTEL_INFO(dev)->gen >= 6)
-		gen6_rps_busy(dev_priv);
-	dev_priv->mm.busy = true;
-}
-
-void intel_mark_idle(struct drm_device *dev)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	if (!dev_priv->mm.busy)
-		return;
-
-	dev_priv->mm.busy = false;
-
-	if (INTEL_INFO(dev)->gen >= 6)
-		gen6_rps_idle(dev->dev_private);
-
-	intel_runtime_pm_put(dev_priv);
-}
-
 static void intel_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-- 
2.6.3

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[PATCH] drm/i915: Only start retire worker when idle

[Chris Wilson]

The retire worker is a low frequency task that makes sure we retire
outstanding requests if userspace is being lax. We only need to start it
once as it remains active until the GPU is idle, so do a cheap test
before the more expensive queue_work(). A consequence of this is that we
need correct locking in the worker to make the hot path of request
submission cheap. To keep the symmetry and keep hangcheck strictly bound
by the GPU's wakelock, we move the cancel_sync(hangcheck) to the idle
worker before dropping the wakelock.

v2: Guard against RCU fouling the breadcrumbs bottom-half whilst we kick
the waiter.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
References: https://bugs.freedesktop.org/show_bug.cgi?id=88437
---
 drivers/gpu/drm/i915/i915_drv.c      |  2 -
 drivers/gpu/drm/i915/i915_drv.h      |  2 +-
 drivers/gpu/drm/i915/i915_gem.c      | 90 +++++++++++++++++++++++++-----------
 drivers/gpu/drm/i915/intel_display.c | 29 ------------
 4 files changed, 64 insertions(+), 59 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index ba91f65b6082..0f79ee1d35a2 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1472,8 +1472,6 @@ static int intel_runtime_suspend(struct device *device)
 	i915_gem_release_all_mmaps(dev_priv);
 	mutex_unlock(&dev->struct_mutex);
 
-	cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work);
-
 	intel_guc_suspend(dev);
 
 	intel_suspend_gt_powersave(dev);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index bbaa12e85c68..9350ce1f0bfa 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -3001,7 +3001,7 @@ int __must_check i915_gem_set_seqno(struct drm_device *dev, u32 seqno);
 struct drm_i915_gem_request *
 i915_gem_find_active_request(struct intel_engine_cs *ring);
 
-bool i915_gem_retire_requests(struct drm_device *dev);
+void i915_gem_retire_requests(struct drm_device *dev);
 void i915_gem_retire_requests_ring(struct intel_engine_cs *ring);
 
 static inline u32 i915_reset_counter(struct i915_gpu_error *error)
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 5719e8d9e33b..2350e00f2e45 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2495,6 +2495,48 @@ i915_gem_get_seqno(struct drm_device *dev, u32 *seqno)
 	return 0;
 }
 
+static void i915_gem_mark_busy(struct drm_i915_private *dev_priv)
+{
+	if (dev_priv->mm.busy)
+		return;
+
+	intel_runtime_pm_get_noresume(dev_priv);
+
+	i915_update_gfx_val(dev_priv);
+	if (INTEL_INFO(dev_priv)->gen >= 6)
+		gen6_rps_busy(dev_priv);
+
+	queue_delayed_work(dev_priv->wq,
+			   &dev_priv->mm.retire_work,
+			   round_jiffies_up_relative(HZ));
+
+	dev_priv->mm.busy = true;
+}
+
+static void kick_waiters(struct drm_i915_private *dev_priv)
+{
+	struct intel_engine_cs *ring;
+	int i;
+
+	rcu_read_lock();
+	for_each_ring(ring, dev_priv, i)
+		intel_engine_wakeup(ring);
+	rcu_read_unlock();
+}
+
+static void i915_gem_mark_idle(struct drm_i915_private *dev_priv)
+{
+	dev_priv->mm.busy = false;
+
+	if (cancel_delayed_work_sync(&dev_priv->gpu_error.hangcheck_work))
+		kick_waiters(dev_priv);
+
+	if (INTEL_INFO(dev_priv)->gen >= 6)
+		gen6_rps_idle(dev_priv);
+
+	intel_runtime_pm_put(dev_priv);
+}
+
 /*
  * NB: This function is not allowed to fail. Doing so would mean the the
  * request is not being tracked for completion but the work itself is
@@ -2575,10 +2617,7 @@ void __i915_add_request(struct drm_i915_gem_request *request,
 
 	trace_i915_gem_request_add(request);
 
-	queue_delayed_work(dev_priv->wq,
-			   &dev_priv->mm.retire_work,
-			   round_jiffies_up_relative(HZ));
-	intel_mark_busy(dev_priv->dev);
+	i915_gem_mark_busy(dev_priv);
 
 	/* Sanity check that the reserved size was large enough. */
 	intel_ring_reserved_space_end(ringbuf);
@@ -2903,7 +2942,7 @@ i915_gem_retire_requests_ring(struct intel_engine_cs *ring)
 	WARN_ON(i915_verify_lists(ring->dev));
 }
 
-bool
+void
 i915_gem_retire_requests(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
@@ -2929,8 +2968,6 @@ i915_gem_retire_requests(struct drm_device *dev)
 		mod_delayed_work(dev_priv->wq,
 				 &dev_priv->mm.idle_work,
 				 msecs_to_jiffies(100));
-
-	return idle;
 }
 
 static void
@@ -2939,17 +2976,21 @@ i915_gem_retire_work_handler(struct work_struct *work)
 	struct drm_i915_private *dev_priv =
 		container_of(work, typeof(*dev_priv), mm.retire_work.work);
 	struct drm_device *dev = dev_priv->dev;
-	bool idle;
 
 	/* Come back later if the device is busy... */
-	idle = false;
 	if (mutex_trylock(&dev->struct_mutex)) {
-		idle = i915_gem_retire_requests(dev);
+		i915_gem_retire_requests(dev);
 		mutex_unlock(&dev->struct_mutex);
 	}
-	if (!idle) {
+
+	/* Keep the retire handler running until we are finally idle.
+	 * We do not need to do this test under locking as in the worst-case
+	 * we queue the retire worker once too often.
+	 */
+	if (READ_ONCE(dev_priv->mm.busy)) {
 		i915_queue_hangcheck(dev_priv);
-		queue_delayed_work(dev_priv->wq, &dev_priv->mm.retire_work,
+		queue_delayed_work(dev_priv->wq,
+				   &dev_priv->mm.retire_work,
 				   round_jiffies_up_relative(HZ));
 	}
 }
@@ -2963,25 +3004,20 @@ i915_gem_idle_work_handler(struct work_struct *work)
 	struct intel_engine_cs *ring;
 	int i;
 
-	for_each_ring(ring, dev_priv, i)
-		if (!list_empty(&ring->request_list))
-			return;
-
-	/* we probably should sync with hangcheck here, using cancel_work_sync.
-	 * Also locking seems to be fubar here, ring->request_list is protected
-	 * by dev->struct_mutex. */
+	if (!mutex_trylock(&dev->struct_mutex))
+		return;
 
-	intel_mark_idle(dev);
+	for_each_ring(ring, dev_priv, i) {
+		if (!list_empty(&ring->request_list))
+			goto out;
 
-	if (mutex_trylock(&dev->struct_mutex)) {
-		struct intel_engine_cs *ring;
-		int i;
+		i915_gem_batch_pool_fini(&ring->batch_pool);
+	}
 
-		for_each_ring(ring, dev_priv, i)
-			i915_gem_batch_pool_fini(&ring->batch_pool);
+	i915_gem_mark_idle(dev_priv);
 
-		mutex_unlock(&dev->struct_mutex);
-	}
+out:
+	mutex_unlock(&dev->struct_mutex);
 }
 
 /**
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index ffcdc2c631e1..3c3766eab5c4 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10810,35 +10810,6 @@ struct drm_display_mode *intel_crtc_mode_get(struct drm_device *dev,
 	return mode;
 }
 
-void intel_mark_busy(struct drm_device *dev)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	if (dev_priv->mm.busy)
-		return;
-
-	intel_runtime_pm_get(dev_priv);
-	i915_update_gfx_val(dev_priv);
-	if (INTEL_INFO(dev)->gen >= 6)
-		gen6_rps_busy(dev_priv);
-	dev_priv->mm.busy = true;
-}
-
-void intel_mark_idle(struct drm_device *dev)
-{
-	struct drm_i915_private *dev_priv = dev->dev_private;
-
-	if (!dev_priv->mm.busy)
-		return;
-
-	dev_priv->mm.busy = false;
-
-	if (INTEL_INFO(dev)->gen >= 6)
-		gen6_rps_idle(dev->dev_private);
-
-	intel_runtime_pm_put(dev_priv);
-}
-
 static void intel_crtc_destroy(struct drm_crtc *crtc)
 {
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-- 
2.6.4

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[PATCH 30/32] drm/i915: Restore waitboost credit to the synchronous waiter

[Chris Wilson]

Ideally, we want to automagically have the GPU respond to the
instantaneous load by reclocking itself. However, reclocking occurs
relatively slowly, and to the client waiting for a result from the GPU,
too late. To compensate and reduce the client latency, we allow the
first wait from a client to boost the GPU clocks to maximum. This
overcomes the lag in autoreclocking, at the expense of forcing the GPU
clocks too high. So to offset the excessive power usage, we currently
allow a client to only boost the clocks once before we detect the GPU
is idle again. This works reasonably for say the first frame in a
benchmark, but for many more synchronous workloads (like OpenCL) we find
the GPU clocks remain too low. By noting a wait which would idle the GPU
(i.e. we just waited upon the last known request), we can give that
client the idle boost credit (for their next wait) without the 100ms
delay required for us to detect the GPU idle state. The intention is to
boost clients that are stalling in the process of feeding the GPU more
work (and who in doing so let the GPU idle), without granting boost
credits to clients that are throttling themselves (such as compositors).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: "Zou, Nanhai" <nanhai.zou@intel.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
---
 drivers/gpu/drm/i915/i915_gem.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index d1a7a7f8f3ad..a0584cffa7cd 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1340,6 +1340,22 @@ out:
 			*timeout = 0;
 	}
 
+	if (ret == 0 && rps && req->seqno == req->ring->last_submitted_seqno) {
+		/* The GPU is now idle and this client has stalled.
+		 * Since no other client has submitted a request in the
+		 * meantime, assume that this client is the only one
+		 * supplying work to the GPU but is unable to keep that
+		 * work supplied because it is waiting. Since the GPU is
+		 * then never kept fully busy, RPS autoclocking will
+		 * keep the clocks relatively low, causing further delays.
+		 * Compensate by giving the synchronous client credit for
+		 * a waitboost next time.
+		 */
+		spin_lock(&req->i915->rps.client_lock);
+		list_del_init(&rps->link);
+		spin_unlock(&req->i915->rps.client_lock);
+	}
+
 	return ret;
 }
 
-- 
2.6.3

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[PATCH 31/32] drm/i915: Add background commentary to "waitboosting"

[Chris Wilson]

Describe the intent of boosting the GPU frequency to maximum before
waiting on the GPU.

RPS waitboosting was introduced with

commit b29c19b645287f7062e17d70fa4e9781a01a5d88
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Sep 25 17:34:56 2013 +0100

    drm/i915: Boost RPS frequency for CPU stalls

but lacked a concise comment in the code to explain itself.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a0584cffa7cd..56b00bf69d89 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1246,6 +1246,22 @@ int __i915_wait_request(struct drm_i915_gem_request *req,
 	}
 
 	trace_i915_gem_request_wait_begin(req);
+
+	/* This client is about to stall waiting for the GPU. In many cases
+	 * this is undesirable and limits the throughput of the system, as
+	 * many clients cannot continue processing user input/output whilst
+	 * asleep. RPS autotuning may take tens of milliseconds to respond
+	 * to the GPU load and thus incurs additional latency for the client.
+	 * We can circumvent that promoting the GPU frequency to maximum
+	 * before we wait. This makes GPU throttle up much more quickly
+	 * (good for benchmarks), but at a cost of spending more power
+	 * processing the workload (bad for battery). Not all clients even
+	 * want their results immediately and for them we should just let
+	 * the GPU select its own frequency to maximise efficiency.
+	 * To prevent a single client from forcing the clocks too high for
+	 * the whole system, we only allow each client to waitboost once
+	 * in a busy period.
+	 */
 	if (INTEL_INFO(req->i915)->gen >= 6)
 		gen6_rps_boost(req->i915, rps, req->emitted_jiffies);
 
-- 
2.6.3

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[PATCH 32/32] drm/i915: Flush the RPS bottom-half when the GPU idles

[Chris Wilson]

Make sure that the RPS bottom-half is flushed before we set the idle
frequency when we decide the GPU is idle. This should prevent any races
with the bottom-half and setting the idle frequency, and ensures that
the bottom-half is bounded by the GPU's rpm reference taken for when it
is active (i.e. between gen6_rps_busy() and gen6_rps_idle()).

v2: Avoid recursively using the i915->wq - RPS does not touch the
struct_mutex so has no place being on the ordered i915->wq.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
---
 drivers/gpu/drm/i915/i915_irq.c |  2 +-
 drivers/gpu/drm/i915/intel_pm.c | 10 +++++++---
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index e5e307654c66..4cfbd694b3a8 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1609,7 +1609,7 @@ static void gen6_rps_irq_handler(struct drm_i915_private *dev_priv, u32 pm_iir)
 		gen6_disable_pm_irq(dev_priv, pm_iir & dev_priv->pm_rps_events);
 		if (dev_priv->rps.interrupts_enabled) {
 			dev_priv->rps.pm_iir |= pm_iir & dev_priv->pm_rps_events;
-			queue_work(dev_priv->wq, &dev_priv->rps.work);
+			schedule_work(&dev_priv->rps.work);
 		}
 		spin_unlock(&dev_priv->irq_lock);
 	}
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 570628628a90..f543f897c516 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4401,11 +4401,15 @@ void gen6_rps_busy(struct drm_i915_private *dev_priv)
 
 void gen6_rps_idle(struct drm_i915_private *dev_priv)
 {
-	struct drm_device *dev = dev_priv->dev;
+	/* Flush our bottom-half so that it does not race with us
+	 * setting the idle frequency and so that it is bounded by
+	 * our rpm wakeref.
+	 */
+	flush_work(&dev_priv->rps.work);
 
 	mutex_lock(&dev_priv->rps.hw_lock);
 	if (dev_priv->rps.enabled) {
-		if (IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev))
+		if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv))
 			vlv_set_rps_idle(dev_priv);
 		else
 			gen6_set_rps(dev_priv->dev, dev_priv->rps.idle_freq);
@@ -4443,7 +4447,7 @@ void gen6_rps_boost(struct drm_i915_private *dev_priv,
 		spin_lock_irq(&dev_priv->irq_lock);
 		if (dev_priv->rps.interrupts_enabled) {
 			dev_priv->rps.client_boost = true;
-			queue_work(dev_priv->wq, &dev_priv->rps.work);
+			schedule_work(&dev_priv->rps.work);
 		}
 		spin_unlock_irq(&dev_priv->irq_lock);
 
-- 
2.6.3

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