On 30/09/2024 14:07, Christian König wrote:
Am 30.09.24 um 15:01 schrieb Tvrtko Ursulin:
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.
Ok going to revert that.
Thank you, and sorry for the trouble!
I also just realized that we don't need to change anything. The rq can't
change as soon as there is a job armed for it.
So having the increment right before pushing the armed job to the entity
was actually correct in the first place.
Are you sure? Two threads racing to arm and push on the same entity?
T1 T2
arm job
rq1 selected
..
push job arm job
inc score rq1
spsc_queue_count check passes
--- just before T1 spsc_queue_push ---
changed to rq2
spsc_queue_push
if (first)
resamples entity->rq
queues rq2
Where rq1 and rq2 belong to different schedulers.
Regards,
Tvrtko
Regards,
Christian.
Regards,
Tvrtko
drm_sched_rq_add_entity(rq, entity);
spin_unlock(&entity->rq_lock);
