[PATCH v9 2/6] drm/i915: Convert requests to use struct fence

John.C.Harrison
2016-06-01T17:08:30Z

From: John Harrison <John.C.Harrison@Intel.com>

There is a construct in the linux kernel called 'struct fence' that is
intended to keep track of work that is executed on hardware. I.e. it
solves the basic problem that the drivers 'struct
drm_i915_gem_request' is trying to address. The request structure does
quite a lot more than simply track the execution progress so is very
definitely still required. However, the basic completion status side
could be updated to use the ready made fence implementation and gain
all the advantages that provides.

This patch makes the first step of integrating a struct fence into the
request. It replaces the explicit reference count with that of the
fence. It also replaces the 'is completed' test with the fence's
equivalent. Currently, that simply chains on to the original request
implementation. A future patch will improve this.

v3: Updated after review comments by Tvrtko Ursulin. Added fence
context/seqno pair to the debugfs request info. Renamed fence 'driver
name' to just 'i915'. Removed BUG_ONs.

v5: Changed seqno format in debugfs to %x rather than %u as that is
apparently the preferred appearance. Line wrapped some long lines to
keep the style checker happy.

v6: Updated to newer nigthly and resolved conflicts. The biggest issue
was with the re-worked busy spin precursor to waiting on a request. In
particular, the addition of a 'request_started' helper function. This
has no corresponding concept within the fence framework. However, it
is only ever used in one place and the whole point of that place is to
always directly read the seqno for absolutely lowest latency possible.
So the simple solution is to just make the seqno test explicit at that
point now rather than later in the series (it was previously being
done anyway when fences become interrupt driven).

v7: Rebased to newer nightly - lots of ring -> engine renaming and
interface change to get_seqno().

v8: Rebased to newer nightly - no longer needs to worry about mutex
locking in the request free code path. Moved to after fence timeline
patch so no longer needs to add a horrid hack timeline.

Removed commented out code block. Added support for possible RCU usage
of fence object (Review comments by Maarten Lankhorst).

For: VIZ-5190
Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
---
drivers/gpu/drm/i915/i915_debugfs.c | 5 +-
drivers/gpu/drm/i915/i915_drv.h | 43 +++++---------
drivers/gpu/drm/i915/i915_gem.c | 101 +++++++++++++++++++++++++++++---
drivers/gpu/drm/i915/intel_lrc.c | 1 +
drivers/gpu/drm/i915/intel_ringbuffer.c | 1 +
drivers/gpu/drm/i915/intel_ringbuffer.h | 2 +
6 files changed, 115 insertions(+), 38 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index ac7e569..844cc4b 100644
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -767,11 +767,12 @@ static int i915_gem_request_info(struct seq_file *m, void *data)
task = NULL;
if (req->pid)
task = pid_task(req->pid, PIDTYPE_PID);
- seq_printf(m, " %x @ %d: %s [%d]\n",
+ seq_printf(m, " %x @ %d: %s [%d], fence = %x:%x\n",
req->seqno,
(int) (jiffies - req->emitted_jiffies),
task ? task->comm : "<unknown>",
- task ? task->pid : -1);
+ task ? task->pid : -1,
+ req->fence.context, req->fence.seqno);
rcu_read_unlock();
}

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index a5f8ad8..905feae 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -42,6 +42,7 @@
#include <linux/kref.h>
#include <linux/pm_qos.h>
#include <linux/shmem_fs.h>
+#include <linux/fence.h>

#include <drm/drmP.h>
#include <drm/intel-gtt.h>
@@ -2353,7 +2354,11 @@ static inline struct scatterlist *__sg_next(struct scatterlist *sg)
* initial reference taken using kref_init
*/
struct drm_i915_gem_request {
- struct kref ref;
+ /**
+ * Underlying object for implementing the signal/wait stuff.
+ */
+ struct fence fence;
+ struct rcu_head rcu_head;

/** On Which ring this request was generated */
struct drm_i915_private *i915;
@@ -2455,7 +2460,13 @@ struct drm_i915_gem_request {
struct drm_i915_gem_request * __must_check
i915_gem_request_alloc(struct intel_engine_cs *engine,
struct i915_gem_context *ctx);
-void i915_gem_request_free(struct kref *req_ref);
+
+static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
+ bool lazy_coherency)
+{
+ return fence_is_signaled(&req->fence);
+}
+
int i915_gem_request_add_to_client(struct drm_i915_gem_request *req,
struct drm_file *file);

@@ -2475,14 +2486,14 @@ static inline struct drm_i915_gem_request *
i915_gem_request_reference(struct drm_i915_gem_request *req)
{
if (req)
- kref_get(&req->ref);
+ fence_get(&req->fence);
return req;
}

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,
@@ -2498,12 +2509,6 @@ static inline void i915_gem_request_assign(struct drm_i915_gem_request **pdst,
}

/*
- * 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.
*/
struct drm_i915_cmd_descriptor {
@@ -3211,24 +3216,6 @@ 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)
-{
- if (!lazy_coherency && req->engine->irq_seqno_barrier)
- req->engine->irq_seqno_barrier(req->engine);
- return i915_seqno_passed(req->engine->get_seqno(req->engine),
- req->previous_seqno);
-}
-
-static inline bool i915_gem_request_completed(struct drm_i915_gem_request *req,
- bool lazy_coherency)
-{
- if (!lazy_coherency && req->engine->irq_seqno_barrier)
- req->engine->irq_seqno_barrier(req->engine);
- return i915_seqno_passed(req->engine->get_seqno(req->engine),
- req->seqno);
-}
-
int __must_check i915_gem_get_seqno(struct drm_i915_private *dev_priv, 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 57d3593..b67fd7c 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -1170,6 +1170,7 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
{
unsigned long timeout;
unsigned cpu;
+ uint32_t seqno;

/* When waiting for high frequency requests, e.g. during synchronous
* rendering split between the CPU and GPU, the finite amount of time
@@ -1185,12 +1186,14 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
return -EBUSY;

/* Only spin if we know the GPU is processing this request */
- if (!i915_gem_request_started(req, true))
+ seqno = req->engine->get_seqno(req->engine);
+ if (!i915_seqno_passed(seqno, req->previous_seqno))
return -EAGAIN;

timeout = local_clock_us(&cpu) + 5;
while (!need_resched()) {
- if (i915_gem_request_completed(req, true))
+ seqno = req->engine->get_seqno(req->engine);
+ if (i915_seqno_passed(seqno, req->seqno))
return 0;

if (signal_pending_state(state, current))
@@ -1202,7 +1205,10 @@ static int __i915_spin_request(struct drm_i915_gem_request *req, int state)
cpu_relax_lowlatency();
}

- if (i915_gem_request_completed(req, false))
+ if (req->engine->irq_seqno_barrier)
+ req->engine->irq_seqno_barrier(req->engine);
+ seqno = req->engine->get_seqno(req->engine);
+ if (i915_seqno_passed(seqno, req->seqno))
return 0;

return -EAGAIN;
@@ -2736,13 +2742,89 @@ static void i915_set_reset_status(struct drm_i915_private *dev_priv,
}
}

-void i915_gem_request_free(struct kref *req_ref)
+static void i915_gem_request_free_rcu(struct rcu_head *head)
{
- struct drm_i915_gem_request *req = container_of(req_ref,
- typeof(*req), ref);
+ struct drm_i915_gem_request *req;
+
+ req = container_of(head, typeof(*req), rcu_head);
kmem_cache_free(req->i915->requests, req);
}

+static void i915_gem_request_free(struct fence *req_fence)
+{
+ struct drm_i915_gem_request *req;
+
+ req = container_of(req_fence, typeof(*req), fence);
+ call_rcu(&req->rcu_head, i915_gem_request_free_rcu);
+}
+
+static bool i915_gem_request_enable_signaling(struct fence *req_fence)
+{
+ /* Interrupt driven fences are not implemented yet.*/
+ WARN(true, "This should not be called!");
+ return true;
+}
+
+static bool i915_gem_request_is_completed(struct fence *req_fence)
+{
+ struct drm_i915_gem_request *req = container_of(req_fence,
+ typeof(*req), fence);
+ u32 seqno;
+
+ seqno = req->engine->get_seqno(req->engine);
+
+ return i915_seqno_passed(seqno, req->seqno);
+}
+
+static const char *i915_gem_request_get_driver_name(struct fence *req_fence)
+{
+ return "i915";
+}
+
+static const char *i915_gem_request_get_timeline_name(struct fence *req_fence)
+{
+ struct drm_i915_gem_request *req;
+ struct i915_fence_timeline *timeline;
+
+ req = container_of(req_fence, typeof(*req), fence);
+ timeline = &req->ctx->engine[req->engine->id].fence_timeline;
+
+ return timeline->name;
+}
+
+static void i915_gem_request_timeline_value_str(struct fence *req_fence,
+ char *str, int size)
+{
+ struct drm_i915_gem_request *req;
+
+ req = container_of(req_fence, typeof(*req), fence);
+
+ /* Last signalled timeline value ??? */
+ snprintf(str, size, "? [%d]"/*, timeline->value*/,
+ req->engine->get_seqno(req->engine));
+}
+
+static void i915_gem_request_fence_value_str(struct fence *req_fence,
+ char *str, int size)
+{
+ struct drm_i915_gem_request *req;
+
+ req = container_of(req_fence, typeof(*req), fence);
+
+ snprintf(str, size, "%d [%d]", req->fence.seqno, req->seqno);
+}
+
+static const struct fence_ops i915_gem_request_fops = {
+ .enable_signaling = i915_gem_request_enable_signaling,
+ .signaled = i915_gem_request_is_completed,
+ .wait = fence_default_wait,
+ .release = i915_gem_request_free,
+ .get_driver_name = i915_gem_request_get_driver_name,
+ .get_timeline_name = i915_gem_request_get_timeline_name,
+ .fence_value_str = i915_gem_request_fence_value_str,
+ .timeline_value_str = i915_gem_request_timeline_value_str,
+};
+
int i915_create_fence_timeline(struct drm_device *dev,
struct i915_gem_context *ctx,
struct intel_engine_cs *engine)
@@ -2770,7 +2852,7 @@ int i915_create_fence_timeline(struct drm_device *dev,
return 0;
}

-unsigned i915_fence_timeline_get_next_seqno(struct i915_fence_timeline *timeline)
+static unsigned i915_fence_timeline_get_next_seqno(struct i915_fence_timeline *timeline)
{
unsigned seqno;

@@ -2814,13 +2896,16 @@ __i915_gem_request_alloc(struct intel_engine_cs *engine,
if (ret)
goto err;

- kref_init(&req->ref);
req->i915 = dev_priv;
req->engine = engine;
req->reset_counter = reset_counter;
req->ctx = ctx;
i915_gem_context_reference(req->ctx);

+ fence_init(&req->fence, &i915_gem_request_fops, &engine->fence_lock,
+ ctx->engine[engine->id].fence_timeline.fence_context,
+ i915_fence_timeline_get_next_seqno(&ctx->engine[engine->id].fence_timeline));
+
/*
* Reserve space in the ring buffer for all the commands required to
* eventually emit this request. This is to guarantee that the
diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
index 14bcfb7..f126bcb 100644
--- a/drivers/gpu/drm/i915/intel_lrc.c
+++ b/drivers/gpu/drm/i915/intel_lrc.c
@@ -2030,6 +2030,7 @@ logical_ring_setup(struct drm_device *dev, enum intel_engine_id id)
INIT_LIST_HEAD(&engine->buffers);
INIT_LIST_HEAD(&engine->execlist_queue);
spin_lock_init(&engine->execlist_lock);
+ spin_lock_init(&engine->fence_lock);

tasklet_init(&engine->irq_tasklet,
intel_lrc_irq_handler, (unsigned long)engine);
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 8d35a39..fbd3f12 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -2254,6 +2254,7 @@ static int intel_init_ring_buffer(struct drm_device *dev,
INIT_LIST_HEAD(&engine->request_list);
INIT_LIST_HEAD(&engine->execlist_queue);
INIT_LIST_HEAD(&engine->buffers);
+ spin_lock_init(&engine->fence_lock);
i915_gem_batch_pool_init(dev, &engine->batch_pool);
memset(engine->semaphore.sync_seqno, 0,
sizeof(engine->semaphore.sync_seqno));
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index b33c876..3f39daf 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -345,6 +345,8 @@ struct intel_engine_cs {
* to encode the command length in the header).
*/
u32 (*get_cmd_length_mask)(u32 cmd_header);
+
+ spinlock_t fence_lock;
};

static inline bool
--
1.9.1