6.13-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra peterz@infradead.org
[ Upstream commit 2a77e4be12cb58bbf774e7c717c8bb80e128b7a4 ]
There are 3 sites using set_next_buddy() and only one is conditional on NEXT_BUDDY, the other two sites are unconditional; to note:
- yield_to_task() - cgroup dequeue / pick optimization
However, having NEXT_BUDDY control both the wakeup-preemption and the picking side of things means its near useless.
Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy") Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20241129101541.GA33464@noisy.programming.kicks-ass... Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/fair.c | 4 ++-- kernel/sched/features.h | 9 +++++++++ 2 files changed, 11 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 26958431deb7a..808010430a16e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5538,9 +5538,9 @@ static struct sched_entity * pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq) { /* - * Enabling NEXT_BUDDY will affect latency but not fairness. + * Picking the ->next buddy will affect latency but not fairness. */ - if (sched_feat(NEXT_BUDDY) && + if (sched_feat(PICK_BUDDY) && cfs_rq->next && entity_eligible(cfs_rq, cfs_rq->next)) { /* ->next will never be delayed */ SCHED_WARN_ON(cfs_rq->next->sched_delayed); diff --git a/kernel/sched/features.h b/kernel/sched/features.h index a3d331dd2d8ff..3c12d9f93331d 100644 --- a/kernel/sched/features.h +++ b/kernel/sched/features.h @@ -31,6 +31,15 @@ SCHED_FEAT(PREEMPT_SHORT, true) */ SCHED_FEAT(NEXT_BUDDY, false)
+/* + * Allow completely ignoring cfs_rq->next; which can be set from various + * places: + * - NEXT_BUDDY (wakeup preemption) + * - yield_to_task() + * - cgroup dequeue / pick + */ +SCHED_FEAT(PICK_BUDDY, true) + /* * Consider buddies to be cache hot, decreases the likeliness of a * cache buddy being migrated away, increases cache locality.