[PATCH v2 0/2] drm/sched: Introduce more locking to entity

[Philipp Stanner <phasta@kernel.org>]

This is for now based on drm-misc-fixes. I send it out so we can get
consensus for our work in the upcoming cycle.

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...


Tested with drm-sched-unit tests. I'm a bit busy right now, but wanted
to show you guys the idea. Before merging I'd test it more exhaustively
with Nouveau.

Greetings,
Philipp

[1] https://lore.kernel.org/dri-devel/20260611123423.39819-1-tvrtko.ursulin@igalia.com/
[2] https://lore.kernel.org/dri-devel/20260626081942.2122144-2-phasta@kernel.org/

Philipp Stanner (2):
  drm/sched: Lock drm_sched_rq_pop_entity() externally
  drm/sched: Protect entity->last_scheduled with spinlock

 drivers/gpu/drm/scheduler/sched_entity.c | 52 ++++++++++--------------
 drivers/gpu/drm/scheduler/sched_rq.c     |  4 +-
 include/drm/gpu_scheduler.h              | 10 ++---
 3 files changed, 28 insertions(+), 38 deletions(-)


base-commit: 9a11db68872055e6ead919bad04d6330851c522d
-- 
2.55.0