[tip:sched/core] sched/fair: Kick nohz balance if rq->misfit_task_load

[tip-bot for Valentin Schneider <tipbot@zytor.com>]

Commit-ID:  5fbdfae5221a5208ed8e7653fc1c4b31de420f74
Gitweb:     https://git.kernel.org/tip/5fbdfae5221a5208ed8e7653fc1c4b31de420f74
Author:     Valentin Schneider <valentin.schneider@arm.com>
AuthorDate: Wed, 4 Jul 2018 11:17:43 +0100
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Mon, 10 Sep 2018 11:05:51 +0200

sched/fair: Kick nohz balance if rq->misfit_task_load

There already are a few conditions in nohz_kick_needed() to ensure
a nohz kick is triggered, but they are not enough for some misfit
task scenarios. Excluding asym packing, those are:

 - rq->nr_running >=2: Not relevant here because we are running a
   misfit task, it needs to be migrated regardless and potentially through
   active balance.

 - sds->nr_busy_cpus > 1: If there is only the misfit task being run
   on a group of low capacity CPUs, this will be evaluated to False.

 - rq->cfs.h_nr_running >=1 && check_cpu_capacity(): Not relevant here,
   misfit task needs to be migrated regardless of rt/IRQ pressure

As such, this commit adds an rq->misfit_task_load condition to trigger a
nohz kick.

The idea to kick a nohz balance for misfit tasks originally came from
Leo Yan <leo.yan@linaro.org>, and a similar patch was submitted for
the Android Common Kernel - see:

  https://lists.linaro.org/pipermail/eas-dev/2016-September/000551.html

Signed-off-by: Valentin Schneider <valentin.schneider@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: vincent.guittot@linaro.org
Link: http://lkml.kernel.org/r/1530699470-29808-6-git-send-email-morten.rasmussen@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 24fe39e57bc3..e08287d3806f 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9135,7 +9135,7 @@ static void nohz_balancer_kick(struct rq *rq)
 	if (time_before(now, nohz.next_balance))
 		goto out;
 
-	if (rq->nr_running >= 2) {
+	if (rq->nr_running >= 2 || rq->misfit_task_load) {
 		flags = NOHZ_KICK_MASK;
 		goto out;
 	}