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

Christian König <ckoenig.leichtzumerken@xxxxxxxxx> · Tue, 10 Sep 2024 11:08:00 +0200

Am 09.09.24 um 19:19 schrieb Tvrtko Ursulin:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>

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@xxxxxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Alex Deucher <alexander.deucher@xxxxxxx>
Cc: Luben Tuikov <ltuikov89@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: Philipp Stanner <pstanner@xxxxxxxxxx>
---
  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,







