sched: Micro optimization in pick_next_task() and in check_preempt_curr() (aa93cd53) · Commits · 戴 / test

This introduces an optimization based on xxx_sched_class addresses in two hot scheduler functions: pick_next_task() and check_preempt_curr(). It is possible to compare pointers to sched classes to check, which of them has a higher priority, instead of current iterations using for_each_class(). One more result of the patch is that size of object file becomes a little less (excluding added BUG_ON(), which goes in __init section): $size kernel/sched/core.o text data bss dec hex filename before: 66446 18957 676 86079 1503f kernel/sched/core.o after: 66398 18957 676 86031 1500f kernel/sched/core.o Signed-off-by:

Kirill Tkhai <ktkhai@virtuozzo.com> Signed-off-by:

Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by:

Peter Zijlstra (Intel) <peterz@infradead.org> Link: http://lkml.kernel.org/r/711a9c4b-ff32-1136-b848-17c622d548f3@yandex.ru

kernel/sched/core.c

+4 −15

Original line number	Diff line number	Diff line
		@@ -1412,20 +1412,10 @@ static inline void check_class_changed(struct rq rq, struct task_struct p,

		void check_preempt_curr(struct rq rq, struct task_struct p, int flags)
		{
		const struct sched_class *class;

		if (p->sched_class == rq->curr->sched_class) {
		if (p->sched_class == rq->curr->sched_class)
		rq->curr->sched_class->check_preempt_curr(rq, p, flags);
		} else {
		for_each_class(class) {
		if (class == rq->curr->sched_class)
		break;
		if (class == p->sched_class) {
		else if (p->sched_class > rq->curr->sched_class)
		resched_curr(rq);
		break;
		}
		}
		}

		/*
		* A queue event has occurred, and we're going to schedule. In
		@@ -4003,8 +3993,7 @@ pick_next_task(struct rq rq, struct task_struct prev, struct rq_flags *rf)
		* higher scheduling class, because otherwise those loose the
		* opportunity to pull in more work from other CPUs.
		*/
		if (likely((prev->sched_class == &idle_sched_class \|\|
		prev->sched_class == &fair_sched_class) &&
		if (likely(prev->sched_class <= &fair_sched_class &&
		rq->nr_running == rq->cfs.h_nr_running)) {

		p = pick_next_task_fair(rq, prev, rf);

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