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sched/fair: Set next buddy for preempt short

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If a shorter slice task can preempt current at wakeup, we make sure that
the decision will not be overwritten in between by setting the task as the
next buddy. This still implies that the waking task remains eligible when
the scheduler will actually pick the next task to run.

Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://patch.msgid.link/20260624151229.1710703-2-vincent.guittot@linaro.org
This commit is contained in:
Vincent Guittot
2026-06-30 10:56:54 +02:00
committed by Peter Zijlstra
parent 3cd1f657fa
commit 8f97b627ff
1 changed files with 10 additions and 1 deletions
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kernel/sched/fair.c
+10 -1
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@@ -9757,6 +9757,15 @@ static inline bool set_preempt_buddy(struct cfs_rq *cfs_rq, struct sched_entity
return true;
}
static inline bool set_short_buddy(struct cfs_rq *cfs_rq, struct sched_entity *pse)
{
if (cfs_rq->next && cfs_rq->next->slice < pse->slice)
return false;
set_next_buddy(cfs_rq, pse);
return true;
}
/*
* WF_SYNC|WF_TTWU indicates the waker expects to sleep but it is not
* strictly enforced because the hint is either misunderstood or
@@ -9931,7 +9940,7 @@ pick:
preempt:
if (preempt_action == PREEMPT_WAKEUP_SHORT) {
cancel_protect_slice(se);
clear_buddies(cfs_rq, se);
set_short_buddy(cfs_rq, pse);
}
resched_curr_lazy(rq);