Re: [PATCH v3 0/3] drm/sched: Introduce more locking to entity

[Tvrtko Ursulin]

On 10/09/2026 08:59, Philipp Stanner wrote:
> Changes since v2:
>    - Fix ordering bug between spsc_queue_pop() and
>      drm_sched_rq_pop_entity().
>
> Changes since v1:
>    - Remove a bunch of patches; make this series only about locking
>      entity->last_scheduled. The rest shall be done in separate patches
>      and series. Consequently, also do not lock spsc_queue, yet.
>    - Move lock-cycle patch to first position. (Tvrtko)
>
>
> Both Tvrtko [1] and I [2] have recently proposed some improvals for
> drm_sched.
>
> While taking Tvrtko's feedback into account for my patch, I realized
> that both his and my patch can be fully replaced with a bigger and far
> more beautiful series.
>
> If I am not mistaken, it turns out that the entire entity->entity_idle
> completion is also nothing but a workaround around the grave mistake of
> not using the greatest helper with parallel programming that exists in
> computer science: Locking.
>
> This series adds locking to the last_scheduled field and all checks
> related to detect the idleness of the entity. As before, the
> job_scheduled event queue causes the periodic checks.
>
> This way, we can get rid of memory barriers, RCU, a few lines of code,
> make things more readable, understandable...
>
> Greetings,
> Philipp
>
> [1] https://lore.kernel.org/dri-devel/20260611123423.39819-1-tvrtko.ursulin@xxxxxxxxxx/
> [2] https://lore.kernel.org/dri-devel/20260626081942.2122144-2-phasta@xxxxxxxxxx/
>
> Philipp Stanner (3):
>    drm/sched: Lock drm_sched_rq_pop_entity() externally
>    drm/sched: Lock spsc_queue_pop() in drm_sched_entity_pop_job()

FWIW if you could review 
https://lore.kernel.org/dri-devel/20260907130527.52530-1-tvrtko.ursulin@xxxxxxxxxx/ 
you could drop the first two patches from your series. Extra benefit is 
that patch fixes a bug and has been tested by the user.

Regards,

Tvrtko

>    drm/sched: Protect entity->last_scheduled with spinlock
>
>   drivers/gpu/drm/scheduler/sched_entity.c | 53 ++++++++++--------------
>   drivers/gpu/drm/scheduler/sched_rq.c     |  4 +-
>   include/drm/gpu_scheduler.h              | 10 ++---
>   3 files changed, 28 insertions(+), 39 deletions(-)