Re: [PATCH] drm/sched: Don't disturb the entity when in RR-mode scheduling

[Luben Tuikov <ltuikov89@gmail.com>]

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On 2023-11-07 06:48, Matthew Brost wrote:
> On Mon, Nov 06, 2023 at 11:10:21PM -0500, Luben Tuikov wrote:
>> Don't call drm_sched_select_entity() in drm_sched_run_job_queue().  In fact,
>> rename __drm_sched_run_job_queue() to just drm_sched_run_job_queue(), and let
>> it do just that, schedule the work item for execution.
>>
>> The problem is that drm_sched_run_job_queue() calls drm_sched_select_entity()
>> to determine if the scheduler has an entity ready in one of its run-queues,
>> and in the case of the Round-Robin (RR) scheduling, the function
>> drm_sched_rq_select_entity_rr() does just that, selects the _next_ entity
>> which is ready, sets up the run-queue and completion and returns that
>> entity. The FIFO scheduling algorithm is unaffected.
>>
>> Now, since drm_sched_run_job_work() also calls drm_sched_select_entity(), then
>> in the case of RR scheduling, that would result in drm_sched_select_entity()
>> having been called twice, which may result in skipping a ready entity if more
>> than one entity is ready. This commit fixes this by eliminating the call to
>> drm_sched_select_entity() from drm_sched_run_job_queue(), and leaves it only
>> in drm_sched_run_job_work().
>>
>> v2: Rebased on top of Tvrtko's renames series of patches. (Luben)
>>     Add fixes-tag. (Tvrtko)
>>
>> Signed-off-by: Luben Tuikov <ltuikov89@gmail.com>
>> Fixes: f7fe64ad0f22ff ("drm/sched: Split free_job into own work item")
> 
> Reviewed-by: Matthew Brost <matthew.brost@intel.com>

Thank you, sir!
-- 
Regards,
Luben

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