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

Maarten Lankhorst
2016-06-07T11:42:05Z

Op 02-06-16 om 13:07 schreef Tvrtko Ursulin:
>
> On 01/06/16 18:07, John.C.Harrison@Intel.com wrote:
>> 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>
>
> Was it an r-b or an ack from Jesse? If the former does it need a "(v?)" suffix, depending on the amount of code changes after his r-b?
>
>> ---
>> 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",
>
> In the previous patch fence context and seqno were %d in the timeline->name so it would probably be more consistent.
>
>> 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);
req->fence.context is 64-bits, will probably cause a compiler warning.
>> 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;
fenece.rcu can be used, no need to duplicate. :)
>> /** 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);
>> +}
>
> I would squash the following patch into this one, it makes no sense to keep a function with an unused parameter. And fewer patches in the series makes it less scary to review. :) Of course if they are also not too big. :D
It's easier to read with all the function parameter changes in a separate patch.
>> +
>> 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*/,
>
> Reference to timeline->value a leftover from the past?
>
> Is the string format defined by the API? Asking because "? [%d]" looks intriguing.
>
>> + 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);
>
> Is it OK to put req->seqno in this one? OR it is just for debug anyway so it helps us and fence framework does not care?
I think this is used for getting all info from debugfs only, so req->seqno is fine.
>> +}
>> +
>> +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;
>
> Why is this lock per-engine, and not for example per timeline? Aren't fencees living completely isolated in their per-context-per-engine domains? So presumably there is something somewhere which is shared outside that domain to need a lock at the engine level?
All outstanding requests are added to engine->fence_signal_list in patch 4, which means a per engine lock is required.