Messages in this thread Patch in this message | | | Date | Mon, 05 Oct 2020 07:43:21 -0000 | From | "tip-bot2 for Peter Oskolkov" <> | Subject | [tip: sched/core] sched/fair: Tweak pick_next_entity() |
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The following commit has been merged into the sched/core branch of tip:
Commit-ID: 9abb897345ce1d41257567f571a78137c961c405 Gitweb: https://git.kernel.org/tip/9abb897345ce1d41257567f571a78137c961c405 Author: Peter Oskolkov <posk@google.com> AuthorDate: Wed, 30 Sep 2020 10:35:32 -07:00 Committer: Peter Zijlstra <peterz@infradead.org> CommitterDate: Sat, 03 Oct 2020 16:30:52 +02:00
sched/fair: Tweak pick_next_entity()
Currently, pick_next_entity(...) has the following structure (simplified):
[...] if (last_buddy_ok()) result = last_buddy; if (next_buddy_ok()) result = next_buddy; [...]
The intended behavior is to prefer next buddy over last buddy; the current code somewhat obfuscates this, and also wastes cycles checking the last buddy when eventually the next buddy is picked up.
So this patch refactors two 'ifs' above into
[...] if (next_buddy_ok()) result = next_buddy; else if (last_buddy_ok()) result = last_buddy; [...]
Signed-off-by: Peter Oskolkov <posk@google.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot <vincent.guitttot@linaro.org> Link: https://lkml.kernel.org/r/20200930173532.1069092-1-posk@google.com --- kernel/sched/fair.c | 20 ++++++++++---------- 1 file changed, 10 insertions(+), 10 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fc3410b..cec6cf9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -4465,17 +4465,17 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr) se = second; } - /* - * Prefer last buddy, try to return the CPU to a preempted task. - */ - if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) - se = cfs_rq->last; - - /* - * Someone really wants this to run. If it's not unfair, run it. - */ - if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) + if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) { + /* + * Someone really wants this to run. If it's not unfair, run it. + */ se = cfs_rq->next; + } else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) { + /* + * Prefer last buddy, try to return the CPU to a preempted task. + */ + se = cfs_rq->last; + } clear_buddies(cfs_rq, se);
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