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

[Tvrtko Ursulin <tvrtko.ursulin@igalia.com>]

On 09/07/2025 18:22, Matthew Brost wrote:
> 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@igalia.com>
>>>> Cc: Christian König <christian.koenig@amd.com>
>>>> Cc: Danilo Krummrich <dakr@kernel.org>
>>>> Cc: Matthew Brost <matthew.brost@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@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.

Thanks!

Philipp - okay to merge this one?

Regards,

Tvrtko
> 
> Matt
> 
>> Regards,
>>
>> Tvrtko
>>
>>>
>>>> Cc: Philipp Stanner <phasta@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
>>>>
>>