[PATCH v5 04/16] drm/sched: Avoid double re-lock on the job free path
Tvrtko Ursulin
tvrtko.ursulin at igalia.com
Fri Jul 4 13:30:26 UTC 2025
On 04/07/2025 13:56, Philipp Stanner wrote:
> On Fri, 2025-07-04 at 09:29 -0300, Maíra Canal wrote:
>> Hi Tvrtko,
>>
>> On 23/06/25 09:27, 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>
>>> Cc: Philipp Stanner <phasta at kernel.org>
>>> ---
>>> drivers/gpu/drm/scheduler/sched_main.c | 39 +++++++++++----------
>>> -----
>>> 1 file changed, 16 insertions(+), 23 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c
>>> b/drivers/gpu/drm/scheduler/sched_main.c
>>> index 1f077782ec12..c6c26aec07b6 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 +1100,27 @@ 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);
>>> +
>>> + if (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT,
>>> + &next->s_fence-
>>>> finished.flags))
>>
>> Shouldn't we use dma_fence_is_signaled() to keep the same check that
>> we
>> have in drm_sched_run_free_queue()?
>
> There is a paused-ongoing discussion about this function:
>
> https://lore.kernel.org/all/20250522112540.161411-2-phasta@kernel.org/
>
>
> dma_fence_is_signaled() can have side effects by actually signaling,
> instead of just checking.
>
> Not sure if Tvrtko wanted to bypass that behavior here, though.
No, no ulterior motives here. :)
It is ages I wrote this, but now I revisited it, and AFAICT I don't see
that it matters in this case.
It is a scheduler fence which does not implement fence->ops->signaled()
so opportunistic signaling does not come into the picture.
I am happy to change it to dma_fence_is_signaled() if that is the
preference.
Regards,
Tvrtko
>>> + *have_more = true;
>>> +
>>> /* start TO timer for next job */
>>> drm_sched_start_timeout(sched);
>>> }
>>
>>
>
More information about the dri-devel
mailing list