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
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@ -4465,17 +4465,17 @@ pick_next_entity(struct cfs_rq *cfs_rq, struct sched_entity *curr)
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se = second;
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}
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/*
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* Prefer last buddy, try to return the CPU to a preempted task.
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*/
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if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1)
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se = cfs_rq->last;
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/*
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* Someone really wants this to run. If it's not unfair, run it.
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*/
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if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1)
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if (cfs_rq->next && wakeup_preempt_entity(cfs_rq->next, left) < 1) {
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/*
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* Someone really wants this to run. If it's not unfair, run it.
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*/
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se = cfs_rq->next;
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} else if (cfs_rq->last && wakeup_preempt_entity(cfs_rq->last, left) < 1) {
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/*
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* Prefer last buddy, try to return the CPU to a preempted task.
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*/
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se = cfs_rq->last;
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}
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clear_buddies(cfs_rq, se);
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