[PATCH 8/8] drm/sched: Further optimise drm_sched_entity_push_job

[Christian König]

Am 09.09.24 um 19:19 schrieb Tvrtko Ursulin:
> From: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
>
> Having removed one re-lock cycle on the entity->lock in a patch titled
> "drm/sched: Optimise drm_sched_entity_push_job", with only a tiny bit
> larger refactoring we can do the same optimisation on the rq->lock.
> (Currently both drm_sched_rq_add_entity() and
> drm_sched_rq_update_fifo_locked() take and release the same lock.)

I think that goes into the wrong direction.

Probably better to move this here into drm_sched_rq_add_entity():

           if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
              drm_sched_rq_update_fifo_locked(entity, submit_ts);

We can then also drop adding the entity to the rr list when FIFO is in use.

Regards,
Christian.


>
> To achieve this we rename drm_sched_rq_add_entity() to
> drm_sched_rq_add_entity_locked(), making it expect the rq->lock to be
> held, and also add the same expectation to
> drm_sched_rq_update_fifo_locked().
>
> For more stream-lining we also add the run-queue as an explicit parameter
> to drm_sched_rq_remove_fifo_locked() to avoid both callers and callee
> having to dereference entity->rq.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at igalia.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Alex Deucher <alexander.deucher at amd.com>
> Cc: Luben Tuikov <ltuikov89 at gmail.com>
> Cc: Matthew Brost <matthew.brost at intel.com>
> Cc: Philipp Stanner <pstanner at redhat.com>
> ---
>   drivers/gpu/drm/scheduler/sched_entity.c |  7 ++--
>   drivers/gpu/drm/scheduler/sched_main.c   | 41 +++++++++++++-----------
>   include/drm/gpu_scheduler.h              |  7 ++--
>   3 files changed, 31 insertions(+), 24 deletions(-)
>
> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
> index b4c4f9923e0b..2102c726d275 100644
> --- a/drivers/gpu/drm/scheduler/sched_entity.c
> +++ b/drivers/gpu/drm/scheduler/sched_entity.c
> @@ -614,11 +614,14 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
>   		sched = rq->sched;
>   
>   		atomic_inc(sched->score);
> -		drm_sched_rq_add_entity(rq, entity);
> +
> +		spin_lock(&rq->lock);
> +		drm_sched_rq_add_entity_locked(rq, entity);
>   
>   		if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> -			drm_sched_rq_update_fifo_locked(entity, submit_ts);
> +			drm_sched_rq_update_fifo_locked(entity, rq, submit_ts);
>   
> +		spin_unlock(&rq->lock);
>   		spin_unlock(&entity->lock);
>   
>   		drm_sched_wakeup(sched, entity);
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index 937e7d1cfc49..1ccd2aed2d32 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -153,41 +153,44 @@ static __always_inline bool drm_sched_entity_compare_before(struct rb_node *a,
>   	return ktime_before(ent_a->oldest_job_waiting, ent_b->oldest_job_waiting);
>   }
>   
> -static inline void drm_sched_rq_remove_fifo_locked(struct drm_sched_entity *entity)
> +static void drm_sched_rq_remove_fifo_locked(struct drm_sched_entity *entity,
> +					    struct drm_sched_rq *rq)
>   {
> -	struct drm_sched_rq *rq = entity->rq;
> -
>   	if (!RB_EMPTY_NODE(&entity->rb_tree_node)) {
>   		rb_erase_cached(&entity->rb_tree_node, &rq->rb_tree_root);
>   		RB_CLEAR_NODE(&entity->rb_tree_node);
>   	}
>   }
>   
> -void drm_sched_rq_update_fifo_locked(struct drm_sched_entity *entity, ktime_t ts)
> +void drm_sched_rq_update_fifo_locked(struct drm_sched_entity *entity,
> +				     struct drm_sched_rq *rq,
> +				     ktime_t ts)
>   {
>   	lockdep_assert_held(&entity->lock);
> +	lockdep_assert_held(&rq->lock);
>   
> -	spin_lock(&entity->rq->lock);
> -
> -	drm_sched_rq_remove_fifo_locked(entity);
> +	drm_sched_rq_remove_fifo_locked(entity, rq);
>   
>   	entity->oldest_job_waiting = ts;
>   
> -	rb_add_cached(&entity->rb_tree_node, &entity->rq->rb_tree_root,
> +	rb_add_cached(&entity->rb_tree_node, &rq->rb_tree_root,
>   		      drm_sched_entity_compare_before);
> -
> -	spin_unlock(&entity->rq->lock);
>   }
>   
>   void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts)
>   {
> +	struct drm_sched_rq *rq;
> +
>   	/*
>   	 * Both locks need to be grabbed, one to protect from entity->rq change
>   	 * for entity from within concurrent drm_sched_entity_select_rq and the
>   	 * other to update the rb tree structure.
>   	 */
>   	spin_lock(&entity->lock);
> -	drm_sched_rq_update_fifo_locked(entity, ts);
> +	rq = entity->rq;
> +	spin_lock(&rq->lock);
> +	drm_sched_rq_update_fifo_locked(entity, rq, ts);
> +	spin_unlock(&rq->lock);
>   	spin_unlock(&entity->lock);
>   }
>   
> @@ -210,25 +213,23 @@ static void drm_sched_rq_init(struct drm_gpu_scheduler *sched,
>   }
>   
>   /**
> - * drm_sched_rq_add_entity - add an entity
> + * drm_sched_rq_add_entity_locked - add an entity
>    *
>    * @rq: scheduler run queue
>    * @entity: scheduler entity
>    *
>    * Adds a scheduler entity to the run queue.
>    */
> -void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> -			     struct drm_sched_entity *entity)
> +void drm_sched_rq_add_entity_locked(struct drm_sched_rq *rq,
> +				    struct drm_sched_entity *entity)
>   {
> +	lockdep_assert_held(&rq->lock);
> +
>   	if (!list_empty(&entity->list))
>   		return;
>   
> -	spin_lock(&rq->lock);
> -
>   	atomic_inc(rq->sched->score);
>   	list_add_tail(&entity->list, &rq->entities);
> -
> -	spin_unlock(&rq->lock);
>   }
>   
>   /**
> @@ -242,6 +243,8 @@ void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
>   void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
>   				struct drm_sched_entity *entity)
>   {
> +	lockdep_assert_held(&entity->lock);
> +
>   	if (list_empty(&entity->list))
>   		return;
>   
> @@ -254,7 +257,7 @@ void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
>   		rq->current_entity = NULL;
>   
>   	if (drm_sched_policy == DRM_SCHED_POLICY_FIFO)
> -		drm_sched_rq_remove_fifo_locked(entity);
> +		drm_sched_rq_remove_fifo_locked(entity, rq);
>   
>   	spin_unlock(&rq->lock);
>   }
> diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> index 5a1e4c803b90..2ad33e2fe2d2 100644
> --- a/include/drm/gpu_scheduler.h
> +++ b/include/drm/gpu_scheduler.h
> @@ -591,13 +591,14 @@ bool drm_sched_dependency_optimized(struct dma_fence* fence,
>   				    struct drm_sched_entity *entity);
>   void drm_sched_fault(struct drm_gpu_scheduler *sched);
>   
> -void drm_sched_rq_add_entity(struct drm_sched_rq *rq,
> -			     struct drm_sched_entity *entity);
> +void drm_sched_rq_add_entity_locked(struct drm_sched_rq *rq,
> +				    struct drm_sched_entity *entity);
>   void drm_sched_rq_remove_entity(struct drm_sched_rq *rq,
>   				struct drm_sched_entity *entity);
>   
>   void drm_sched_rq_update_fifo(struct drm_sched_entity *entity, ktime_t ts);
> -void drm_sched_rq_update_fifo_locked(struct drm_sched_entity *entity, ktime_t ts);
> +void drm_sched_rq_update_fifo_locked(struct drm_sched_entity *entity,
> +				     struct drm_sched_rq *rq, ktime_t ts);
>   
>   int drm_sched_entity_init(struct drm_sched_entity *entity,
>   			  enum drm_sched_priority priority,