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sched/fair: Untangle NEXT_BUDDY and pick_next_task()

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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.net
This commit is contained in:
Peter Zijlstra 2024-11-29 11:15:41 +01:00
parent 95d9fed3a2
commit 2a77e4be12
2 changed files with 11 additions and 2 deletions
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4
kernel/sched/fair.c
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@ -5630,9 +5630,9 @@ pick_next_entity(struct rq *rq, struct cfs_rq *cfs_rq)
struct sched_entity *se;
/*
* 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);

9
kernel/sched/features.h
View File

@ -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.