On 13/09/2024 17:05, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
Entities run queue can change during drm_sched_entity_push_job() so make
sure to update the score consistently.
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx>
Fixes: d41a39dda140 ("drm/scheduler: improve job distribution with multiple queues")
Cc: Nirmoy Das <nirmoy.das@xxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Luben Tuikov <ltuikov89@xxxxxxxxx>
Cc: Matthew Brost <matthew.brost@xxxxxxxxx>
Cc: David Airlie <airlied@xxxxxxxxx>
Cc: Daniel Vetter <daniel@xxxxxxxx>
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: <stable@xxxxxxxxxxxxxxx> # v5.9+
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Nirmoy Das <nirmoy.das@xxxxxxxxx>
---
drivers/gpu/drm/scheduler/sched_entity.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c
index 76e422548d40..6645a8524699 100644
--- a/drivers/gpu/drm/scheduler/sched_entity.c
+++ b/drivers/gpu/drm/scheduler/sched_entity.c
@@ -586,7 +586,6 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
ktime_t submit_ts;
trace_drm_sched_job(sched_job, entity);
- atomic_inc(entity->rq->sched->score);
WRITE_ONCE(entity->last_user, current->group_leader);
/*
@@ -614,6 +613,7 @@ void drm_sched_entity_push_job(struct drm_sched_job *sched_job)
rq = entity->rq;
sched = rq->sched;
+ atomic_inc(sched->score);
Ugh this is wrong. :(
I was working on some further consolidation and realised this.
It will create an imbalance in score since score is currently supposed
to be accounted twice:
1. +/- 1 for each entity (de-)queued
2. +/- 1 for each job queued/completed
By moving it into the "if (first) branch" it unbalances it.
But it is still true the original placement is racy. It looks like what
is required is an unconditional entity->lock section after
spsc_queue_push. AFAICT that's the only way to be sure entity->rq is set
for the submission at hand.
Question also is, why +/- score in entity add/remove and not just for jobs?
In the meantime patch will need to get reverted.
Regards,
Tvrtko
drm_sched_rq_add_entity(rq, entity);
spin_unlock(&entity->rq_lock);
