Commit 4ad3831a authored Jul 04, 2018 by Chris Redpath Committed by Ingo Molnar Sep 10, 2018

sched/fair: Don't move tasks to lower capacity CPUs unless necessary



When lower capacity CPUs are load balancing and considering to pull
something from a higher capacity group, we should not pull tasks from a
CPU with only one task running as this is guaranteed to impede progress
for that task. If there is more than one task running, load balance in
the higher capacity group would have already made any possible moves to
resolve imbalance and we should make better use of system compute
capacity by moving a task if we still have more than one running.

Signed-off-by: Chris Redpath <chris.redpath@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dietmar.eggemann@arm.com
Cc: gaku.inami.xh@renesas.com
Cc: valentin.schneider@arm.com
Cc: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1530699470-29808-11-git-send-email-morten.rasmussen@arm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 757ffdd7

kernel/sched/fair.c

+11 −0

Original line number	Diff line number	Diff line
		@@ -8423,6 +8423,17 @@ static struct rq find_busiest_queue(struct lb_env env,

		capacity = capacity_of(i);

		/*
		* For ASYM_CPUCAPACITY domains, don't pick a CPU that could
		* eventually lead to active_balancing high->low capacity.
		* Higher per-CPU capacity is considered better than balancing
		* average load.
		*/
		if (env->sd->flags & SD_ASYM_CPUCAPACITY &&
		capacity_of(env->dst_cpu) < capacity &&
		rq->nr_running == 1)
		continue;

		wl = weighted_cpuload(rq);

		/*

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