Re: [Intel-xe] [PATCH v3 11/13] drm/sched: Waiting for pending jobs to complete in scheduler kill

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Sep 12, 2023 at 11:57:30AM +0200, Christian König wrote:
> Am 12.09.23 um 04:16 schrieb Matthew Brost:
> > Wait for pending jobs to be complete before signaling queued jobs. This
> > ensures dma-fence signaling order correct and also ensures the entity is
> > not running on the hardware after drm_sched_entity_flush or
> > drm_sched_entity_fini returns.
> 
> Entities are *not* supposed to outlive the submissions they carry and we
> absolutely *can't* wait for submissions to finish while killing the entity.
> 
> In other words it is perfectly expected that entities doesn't exists any
> more while the submissions they carried are still running on the hardware.
> 
> I somehow better need to document how this working and especially why it is
> working like that.
> 
> This approach came up like four or five times now and we already applied and
> reverted patches doing this.
> 
> For now let's take a look at the source code of drm_sched_entity_kill():
> 
>        /* The entity is guaranteed to not be used by the scheduler */
>         prev = rcu_dereference_check(entity->last_scheduled, true);
>         dma_fence_get(prev);
> 
>         while ((job = to_drm_sched_job(spsc_queue_pop(&entity->job_queue))))
> {
>                 struct drm_sched_fence *s_fence = job->s_fence;
> 
>                 dma_fence_get(&s_fence->finished);
>                 if (!prev || dma_fence_add_callback(prev, &job->finish_cb,
> drm_sched_entity_kill_jobs_cb))
>                         drm_sched_entity_kill_jobs_cb(NULL,
> &job->finish_cb);
> 
>                 prev = &s_fence->finished;
>         }
>         dma_fence_put(prev);
> 
> This ensures the dma-fence signaling order by delegating signaling of the
> scheduler fences into callbacks.
> 

Thanks for the explaination, this code makes more sense now. Agree this
patch is not correct.

This patch really is an RFC for something Nouveau needs, I can delete
this patch in the next rev and let Nouveau run with a slightly different
version if needed.

Matt

> Regards,
> Christian.
> 
> > 
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c |  2 +-
> >   drivers/gpu/drm/scheduler/sched_entity.c    |  7 ++-
> >   drivers/gpu/drm/scheduler/sched_main.c      | 50 ++++++++++++++++++---
> >   include/drm/gpu_scheduler.h                 | 18 ++++++++
> >   4 files changed, 70 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > index fb5dad687168..7835c0da65c5 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_debugfs.c
> > @@ -1873,7 +1873,7 @@ static void amdgpu_ib_preempt_mark_partial_job(struct amdgpu_ring *ring)
> >   	list_for_each_entry_safe(s_job, tmp, &sched->pending_list, list) {
> >   		if (dma_fence_is_signaled(&s_job->s_fence->finished)) {
> >   			/* remove job from ring_mirror_list */
> > -			list_del_init(&s_job->list);
> > +			drm_sched_remove_pending_job(s_job);
> >   			sched->ops->free_job(s_job);
> >   			continue;
> >   		}
> > diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> > index 1dec97caaba3..37557fbb96d0 100644
> > --- a/drivers/gpu/drm/scheduler/sched_entity.c
> > +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> > @@ -104,9 +104,11 @@ int drm_sched_entity_init(struct drm_sched_entity *entity,
> >   	}
> >   	init_completion(&entity->entity_idle);
> > +	init_completion(&entity->jobs_done);
> > -	/* We start in an idle state. */
> > +	/* We start in an idle and jobs done state. */
> >   	complete_all(&entity->entity_idle);
> > +	complete_all(&entity->jobs_done);
> >   	spin_lock_init(&entity->rq_lock);
> >   	spsc_queue_init(&entity->job_queue);
> > @@ -256,6 +258,9 @@ static void drm_sched_entity_kill(struct drm_sched_entity *entity)
> >   	/* Make sure this entity is not used by the scheduler at the moment */
> >   	wait_for_completion(&entity->entity_idle);
> > +	/* Make sure all pending jobs are done */
> > +	wait_for_completion(&entity->jobs_done);
> > +
> >   	/* The entity is guaranteed to not be used by the scheduler */
> >   	prev = rcu_dereference_check(entity->last_scheduled, true);
> >   	dma_fence_get(prev);
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > index 689fb6686e01..ed6f5680793a 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -510,12 +510,52 @@ void drm_sched_resume_timeout(struct drm_gpu_scheduler *sched,
> >   }
> >   EXPORT_SYMBOL(drm_sched_resume_timeout);
> > +/**
> > + * drm_sched_add_pending_job - Add pending job to scheduler
> > + *
> > + * @job: scheduler job to add
> > + * @tail: add to tail of pending list
> > + */
> > +void drm_sched_add_pending_job(struct drm_sched_job *job, bool tail)
> > +{
> > +	struct drm_gpu_scheduler *sched = job->sched;
> > +	struct drm_sched_entity *entity = job->entity;
> > +
> > +	lockdep_assert_held(&sched->job_list_lock);
> > +
> > +	if (tail)
> > +		list_add_tail(&job->list, &sched->pending_list);
> > +	else
> > +		list_add(&job->list, &sched->pending_list);
> > +	if (!entity->pending_job_count++)
> > +		reinit_completion(&entity->jobs_done);
> > +}
> > +EXPORT_SYMBOL(drm_sched_add_pending_job);
> > +
> > +/**
> > + * drm_sched_remove_pending_job - Remove pending job from` scheduler
> > + *
> > + * @job: scheduler job to remove
> > + */
> > +void drm_sched_remove_pending_job(struct drm_sched_job *job)
> > +{
> > +	struct drm_gpu_scheduler *sched = job->sched;
> > +	struct drm_sched_entity *entity = job->entity;
> > +
> > +	lockdep_assert_held(&sched->job_list_lock);
> > +
> > +	list_del_init(&job->list);
> > +	if (!--entity->pending_job_count)
> > +		complete_all(&entity->jobs_done);
> > +}
> > +EXPORT_SYMBOL(drm_sched_remove_pending_job);
> > +
> >   static void drm_sched_job_begin(struct drm_sched_job *s_job)
> >   {
> >   	struct drm_gpu_scheduler *sched = s_job->sched;
> >   	spin_lock(&sched->job_list_lock);
> > -	list_add_tail(&s_job->list, &sched->pending_list);
> > +	drm_sched_add_pending_job(s_job, true);
> >   	spin_unlock(&sched->job_list_lock);
> >   }
> > @@ -538,7 +578,7 @@ static void drm_sched_job_timedout(struct work_struct *work)
> >   		 * drm_sched_cleanup_jobs. It will be reinserted back after sched->thread
> >   		 * is parked at which point it's safe.
> >   		 */
> > -		list_del_init(&job->list);
> > +		drm_sched_remove_pending_job(job);
> >   		spin_unlock(&sched->job_list_lock);
> >   		status = job->sched->ops->timedout_job(job);
> > @@ -589,7 +629,7 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
> >   		 * Add at the head of the queue to reflect it was the earliest
> >   		 * job extracted.
> >   		 */
> > -		list_add(&bad->list, &sched->pending_list);
> > +		drm_sched_add_pending_job(bad, false);
> >   	/*
> >   	 * Iterate the job list from later to  earlier one and either deactive
> > @@ -611,7 +651,7 @@ void drm_sched_stop(struct drm_gpu_scheduler *sched, struct drm_sched_job *bad)
> >   			 * Locking here is for concurrent resume timeout
> >   			 */
> >   			spin_lock(&sched->job_list_lock);
> > -			list_del_init(&s_job->list);
> > +			drm_sched_remove_pending_job(s_job);
> >   			spin_unlock(&sched->job_list_lock);
> >   			/*
> > @@ -1066,7 +1106,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
> >   	if (job && dma_fence_is_signaled(&job->s_fence->finished)) {
> >   		/* remove job from pending_list */
> > -		list_del_init(&job->list);
> > +		drm_sched_remove_pending_job(job);
> >   		/* cancel this job's TO timer */
> >   		cancel_delayed_work(&sched->work_tdr);
> > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > index b7b818cd81b6..7c628f36fe78 100644
> > --- a/include/drm/gpu_scheduler.h
> > +++ b/include/drm/gpu_scheduler.h
> > @@ -233,6 +233,21 @@ struct drm_sched_entity {
> >   	 */
> >   	struct completion		entity_idle;
> > +	/**
> > +	 * @pending_job_count:
> > +	 *
> > +	 * Number of pending jobs.
> > +	 */
> > +	unsigned int                    pending_job_count;
> > +
> > +	/**
> > +	 * @jobs_done:
> > +	 *
> > +	 * Signals when entity has no pending jobs, used to sequence entity
> > +	 * cleanup in drm_sched_entity_fini().
> > +	 */
> > +	struct completion		jobs_done;
> > +
> >   	/**
> >   	 * @oldest_job_waiting:
> >   	 *
> > @@ -656,4 +671,7 @@ struct drm_gpu_scheduler *
> >   drm_sched_pick_best(struct drm_gpu_scheduler **sched_list,
> >   		     unsigned int num_sched_list);
> > +void drm_sched_add_pending_job(struct drm_sched_job *job, bool tail);
> > +void drm_sched_remove_pending_job(struct drm_sched_job *job);
> > +
> >   #endif
>