Re: [PATCH v6 03/15] drm/sched: Avoid double re-lock on the job free path

[Tvrtko Ursulin]

On 08/07/2025 12:22, Philipp Stanner wrote:

On Tue, 2025-07-08 at 10:51 +0100, Tvrtko Ursulin wrote:

Currently the job free work item will lock sched->job_list_lock first
time
to see if there are any jobs, free a single job, and then lock again
to
decide whether to re-queue itself if there are more finished jobs.

Since drm_sched_get_finished_job() already looks at the second job in
the
queue we can simply add the signaled check and have it return the
presence
of more jobs to free to the caller. That way the work item does not
have
to lock the list again and repeat the signaled check.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursu...@igalia.com>
Cc: Christian König <christian.koe...@amd.com>
Cc: Danilo Krummrich <d...@kernel.org>
Cc: Matthew Brost <matthew.br...@intel.com>
Cc: Philipp Stanner <pha...@kernel.org>

This one can be sent separately, like the one for drm_sched_init()
recently, can't it?

Done.

Regards,

Tvrtko

P.

---
  drivers/gpu/drm/scheduler/sched_main.c | 37 ++++++++++--------------
--
  1 file changed, 14 insertions(+), 23 deletions(-)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c
b/drivers/gpu/drm/scheduler/sched_main.c
index 1f077782ec12..1bce0b66f89c 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -366,22 +366,6 @@ static void __drm_sched_run_free_queue(struct
drm_gpu_scheduler *sched)
                queue_work(sched->submit_wq, &sched->work_free_job);
  }

-/**

- * drm_sched_run_free_queue - enqueue free-job work if ready
- * @sched: scheduler instance
- */
-static void drm_sched_run_free_queue(struct drm_gpu_scheduler
*sched)
-{
-       struct drm_sched_job *job;
-
-       spin_lock(&sched->job_list_lock);
-       job = list_first_entry_or_null(&sched->pending_list,
-                                      struct drm_sched_job, list);
-       if (job && dma_fence_is_signaled(&job->s_fence->finished))
-               __drm_sched_run_free_queue(sched);
-       spin_unlock(&sched->job_list_lock);
-}
-
  /**
   * drm_sched_job_done - complete a job
   * @s_job: pointer to the job which is done
@@ -1102,12 +1086,13 @@ drm_sched_select_entity(struct
drm_gpu_scheduler *sched)
   * drm_sched_get_finished_job - fetch the next finished job to be
destroyed
   *
   * @sched: scheduler instance
+ * @have_more: are there more finished jobs on the list
   *
   * Returns the next finished job from the pending list (if there is
one)
   * ready for it to be destroyed.
   */
  static struct drm_sched_job *
-drm_sched_get_finished_job(struct drm_gpu_scheduler *sched)
+drm_sched_get_finished_job(struct drm_gpu_scheduler *sched, bool
*have_more)
  {
        struct drm_sched_job *job, *next;

@@ -1115,22 +1100,25 @@ drm_sched_get_finished_job(struct

drm_gpu_scheduler *sched)

  job = list_first_entry_or_null(&sched->pending_list,

                                       struct drm_sched_job, list);
-
        if (job && dma_fence_is_signaled(&job->s_fence->finished)) {
                /* remove job from pending_list */
                list_del_init(&job->list);

  /* cancel this job's TO timer */

                cancel_delayed_work(&sched->work_tdr);
-               /* make the scheduled timestamp more accurate */
+
+               *have_more = false;
                next = list_first_entry_or_null(&sched-

pending_list,

                                                typeof(*next),
list);
-
                if (next) {
+                       /* make the scheduled timestamp more
accurate */
                        if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
                                     &next->s_fence-

scheduled.flags))

                                next->s_fence->scheduled.timestamp =
                                        dma_fence_timestamp(&job-

s_fence->finished);

+
+                       *have_more = dma_fence_is_signaled(&next-

s_fence->finished);

+
                        /* start TO timer for next job */
                        drm_sched_start_timeout(sched);
                }
@@ -1189,12 +1177,15 @@ static void drm_sched_free_job_work(struct
work_struct *w)
        struct drm_gpu_scheduler *sched =
                container_of(w, struct drm_gpu_scheduler,
work_free_job);
        struct drm_sched_job *job;
+       bool have_more;

- job = drm_sched_get_finished_job(sched);

-       if (job)
+       job = drm_sched_get_finished_job(sched, &have_more);
+       if (job) {
                sched->ops->free_job(job);
+               if (have_more)
+                       __drm_sched_run_free_queue(sched);
+       }

- drm_sched_run_free_queue(sched);

        drm_sched_run_job_queue(sched);
  }