Commit 423d02e1 authored Jun 16, 2020 by Peng Wang Committed by Peter Zijlstra Jun 25, 2020

sched/fair: Optimize dequeue_task_fair()

While looking at enqueue_task_fair and dequeue_task_fair, it occurred
to me that dequeue_task_fair can also be optimized as Vincent described
in commit 7d148be6 ("sched/fair: Optimize enqueue_task_fair()").

When encountering throttled cfs_rq, dequeue_throttle label can ensure
se not to be NULL, and rq->nr_running remains unchanged, so we can also
skip the early balance check.

Signed-off-by: Peng Wang <rocking@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/701eef9a40de93dcf5fe7063fd607bca5db38e05.1592287263.git.rocking@linux.alibaba.com

parent aa93cd53

kernel/sched/fair.c

+3 −3

Original line number	Diff line number	Diff line
		@@ -5624,14 +5624,14 @@ static void dequeue_task_fair(struct rq rq, struct task_struct p, int flags)

		}

		dequeue_throttle:
		if (!se)
		/* At this point se is NULL and we are at root level*/
		sub_nr_running(rq, 1);

		/* balance early to pull high priority tasks */
		if (unlikely(!was_sched_idle && sched_idle_rq(rq)))
		rq->next_balance = jiffies;

		dequeue_throttle:
		util_est_dequeue(&rq->cfs, p, task_sleep);
		hrtick_update(rq);
		}