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

[Matthew Brost]

On Wed, Jul 09, 2025 at 11:49:44AM +0100, Tvrtko Ursulin wrote:
> 
> On 09/07/2025 05:45, Matthew Brost wrote:
> > On Tue, Jul 08, 2025 at 01:20:32PM +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.ursulin at igalia.com>
> > > Cc: Christian König <christian.koenig at amd.com>
> > > Cc: Danilo Krummrich <dakr at kernel.org>
> > > Cc: Matthew Brost <matthew.brost at intel.com>
> > 
> > The patch looks correct, we do have CI failure in a section which
> > stresses scheduling though. Probably noise though. Do you have Intel
> > hardware? I suggest running xe_exec_threads in a loop on either LNL or
> > BMG and see if the CI failure pops. If you don't have hardware, let me
> > know and I can do this.
> > 
> > With a bit of investigation in the CI failure:
> > Reviewed-by: Matthew Brost <matthew.brost at intel.com>
> 
> Thanks! I don't have the HW but I was able to press re-test in the CI so
> lets see. Although at the moment I can't imagine a failure mode like that
> could be caused by this patch.
> 

I ran xe_exec_threads in a loop 20x on BMG without a failure so CI issue
seem unrelated.

Matt 

> Regards,
> 
> Tvrtko
> 
> > 
> > > Cc: Philipp Stanner <phasta at kernel.org>
> > > ---
> > >   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);
> > >   }
> > > -- 
> > > 2.48.0
> > > 
>