drm/sched: Don't disturb the entity when in RR-mode scheduling

Don't call drm_sched_select_entity() in drm_sched_run_job_queue().  In fact,
rename __drm_sched_run_job_queue() to just drm_sched_run_job_queue(), and let
it do just that, schedule the work item for execution.

The problem is that drm_sched_run_job_queue() calls drm_sched_select_entity()
to determine if the scheduler has an entity ready in one of its run-queues,
and in the case of the Round-Robin (RR) scheduling, the function
drm_sched_rq_select_entity_rr() does just that, selects the _next_ entity
which is ready, sets up the run-queue and completion and returns that
entity. The FIFO scheduling algorithm is unaffected.

Now, since drm_sched_run_job_work() also calls drm_sched_select_entity(), then
in the case of RR scheduling, that would result in drm_sched_select_entity()
having been called twice, which may result in skipping a ready entity if more
than one entity is ready. This commit fixes this by eliminating the call to
drm_sched_select_entity() from drm_sched_run_job_queue(), and leaves it only
in drm_sched_run_job_work().

v2: Rebased on top of Tvrtko's renames series of patches. (Luben)
    Add fixes-tag. (Tvrtko)

Signed-off-by: Luben Tuikov <[email protected]>
Fixes: f7fe64a ("drm/sched: Split free_job into own work item")
Reviewed-by: Matthew Brost <[email protected]>
Reviewed-by: Danilo Krummrich <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]

Author: Luben Tuikov

drivers/gpu/drm/scheduler/sched_main.c

@@ -256,10 +256,10 @@ drm_sched_rq_select_entity_fifo(struct drm_sched_rq *rq)
 }
 
 /**
- * __drm_sched_run_job_queue - enqueue run-job work
+ * drm_sched_run_job_queue - enqueue run-job work
  * @sched: scheduler instance
  */
-static void __drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
+static void drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
 {
 	if (!READ_ONCE(sched->pause_submit))
 		queue_work(sched->submit_wq, &sched->work_run_job);
@@ -928,7 +928,7 @@ static bool drm_sched_can_queue(struct drm_gpu_scheduler *sched)
 void drm_sched_wakeup(struct drm_gpu_scheduler *sched)
 {
 	if (drm_sched_can_queue(sched))
-		__drm_sched_run_job_queue(sched);
+		drm_sched_run_job_queue(sched);
 }
 
 /**
@@ -1040,16 +1040,6 @@ drm_sched_pick_best(struct drm_gpu_scheduler **sched_list,
 }
 EXPORT_SYMBOL(drm_sched_pick_best);
 
-/**
- * drm_sched_run_job_queue - enqueue run-job work if there are ready entities
- * @sched: scheduler instance
- */
-static void drm_sched_run_job_queue(struct drm_gpu_scheduler *sched)
-{
-	if (drm_sched_select_entity(sched))
-		__drm_sched_run_job_queue(sched);
-}
-
 /**
  * drm_sched_free_job_work - worker to call free_job
  *