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Commit 71a29aa7 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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sched: Deal with low-load in wake_affine() 



wake_affine() would always fail under low-load situations where
both prev and this were idle, because adding a single task will
always be a significant imbalance, even if there's nothing
around that could balance it.

Deal with this by allowing imbalance when there's nothing you
can do about it.

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent cdd2ab3d

kernel/sched_fair.c

+11 −1
Original line number Diff line number Diff line
@@ -1262,7 +1262,17 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq, 
	tg = task_group(p);

	weight = p->se.load.weight;



	balanced = 100*(tl + effective_load(tg, this_cpu, weight, weight)) <=

	/*

	 * In low-load situations, where prev_cpu is idle and this_cpu is idle

	 * due to the sync cause above having dropped tl to 0, we'll always have

	 * an imbalance, but there's really nothing you can do about that, so

	 * that's good too.

	 *

	 * Otherwise check if either cpus are near enough in load to allow this

	 * task to be woken on this_cpu.

	 */

	balanced = !tl ||

		100*(tl + effective_load(tg, this_cpu, weight, weight)) <=

		imbalance*(load + effective_load(tg, prev_cpu, 0, weight));



	/*