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

[Tvrtko Ursulin]

On 16/07/2025 14:31, Maíra Canal wrote:
> Hi Tvrtko,
> 
> On 16/07/25 05:51, 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 be freed 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: Maíra Canal <mcanal at igalia.com>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: Philipp Stanner <phasta at kernel.org>
>> ---
>> v2:
>>   * Improve commit text and kerneldoc. (Philipp)
>>   * Rename run free work helper. (Philipp)
>>
>> v3:
>>   * Rebase on top of Maira's changes.
>> ---
>>   drivers/gpu/drm/scheduler/sched_main.c | 53 ++++++++++----------------
>>   1 file changed, 21 insertions(+), 32 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/ 
>> scheduler/sched_main.c
>> index e2cda28a1af4..5a550fd76bf0 100644
>> --- a/drivers/gpu/drm/scheduler/sched_main.c
>> +++ b/drivers/gpu/drm/scheduler/sched_main.c
>> @@ -349,34 +349,13 @@ static void drm_sched_run_job_queue(struct 
>> drm_gpu_scheduler *sched)
>>   }
>>   /**
>> - * __drm_sched_run_free_queue - enqueue free-job work
>> - * @sched: scheduler instance
>> - */
>> -static void __drm_sched_run_free_queue(struct drm_gpu_scheduler *sched)
>> -{
>> -    if (!READ_ONCE(sched->pause_submit))
>> -        queue_work(sched->submit_wq, &sched->work_free_job);
>> -}
>> -
>> -/**
>> - * drm_sched_run_free_queue - enqueue free-job work if ready
>> + * drm_sched_run_free_queue - enqueue free-job work
>>    * @sched: scheduler instance
>>    */
>>   static void drm_sched_run_free_queue(struct drm_gpu_scheduler *sched)
>>   {
>> -    struct drm_sched_job *job;
>> -
>> -    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);
> 
> I believe we'd still need this chunk for DRM_GPU_SCHED_STAT_NO_HANG
> (check the comment in drm_sched_job_reinsert_on_false_timeout()). How

You mean the "is there a signaled job in the list check" is needed for 
drm_sched_job_reinsert_on_false_timeout()? Hmm why? Worst case is a 
false positive wakeup on the free worker, no?

> about only deleting drm_sched_run_free_queue_unlocked() and keep using
> __drm_sched_run_free_queue()?

You mean use __drm_sched_run_free_queue() from 
drm_sched_job_reinsert_on_false_timeout()? That is the same as 
drm_sched_run_free_queue() with this patch.

Regards,

Tvrtko

>> -}
>> -
>> -static void drm_sched_run_free_queue_unlocked(struct 
>> drm_gpu_scheduler *sched)
>> -{
>> -    spin_lock(&sched->job_list_lock);
>> -    drm_sched_run_free_queue(sched);
>> -    spin_unlock(&sched->job_list_lock);
>> +    if (!READ_ONCE(sched->pause_submit))
>> +        queue_work(sched->submit_wq, &sched->work_free_job);
>>   }
>>   /**
>> @@ -398,7 +377,7 @@ static void drm_sched_job_done(struct 
>> drm_sched_job *s_job, int result)
>>       dma_fence_get(&s_fence->finished);
>>       drm_sched_fence_finished(s_fence, result);
>>       dma_fence_put(&s_fence->finished);
>> -    __drm_sched_run_free_queue(sched);
>> +    drm_sched_run_free_queue(sched);
>>   }
>>   /**
>> @@ -1134,12 +1113,16 @@ 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
>> + *
>> + * Informs the caller through @have_more whether there are more 
>> finished jobs
>> + * besides the returned one.
>>    *
>>    * 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;
>> @@ -1147,22 +1130,25 @@ 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);
>>           }
>> @@ -1221,12 +1207,15 @@ 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_unlocked(sched);
>>       drm_sched_run_job_queue(sched);
>>   }
>