linux-kernel - [RFCv4 PATCH 33/34] sched: Enable idle balance to pull single task towards cpu with higher capacity

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Message-Id: <1431459549-18343-34-git-send-email-morten.rasmussen@arm.com>
Date:	Tue, 12 May 2015 20:39:08 +0100
From:	Morten Rasmussen <morten.rasmussen@....com>
To:	peterz@...radead.org, mingo@...hat.com
Cc:	vincent.guittot@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, preeti@...ux.vnet.ibm.com,
	mturquette@...aro.org, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org, morten.rasmussen@....com
Subject: [RFCv4 PATCH 33/34] sched: Enable idle balance to pull single task towards cpu with higher capacity

From: Dietmar Eggemann <dietmar.eggemann@....com>

We do not want to miss out on the ability to pull a single remaining
task from a potential source cpu towards an idle destination cpu if the
energy aware system operates above the tipping point.

Add an extra criteria to need_active_balance() to kick off active load
balance if the source cpu is over-utilized and has lower capacity than
the destination cpu.

cc: Ingo Molnar <mingo@...hat.com>
cc: Peter Zijlstra <peterz@...radead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@....com>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
---
 kernel/sched/fair.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 83218e0..8efeb1d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -7527,6 +7527,13 @@ static int need_active_balance(struct lb_env *env)
 			return 1;
 	}
 
+	if ((capacity_of(env->src_cpu) < capacity_of(env->dst_cpu)) &&
+				env->src_rq->cfs.h_nr_running == 1 &&
+				cpu_overutilized(env->src_cpu) &&
+				!cpu_overutilized(env->dst_cpu)) {
+			return 1;
+	}
+
 	return unlikely(sd->nr_balance_failed > sd->cache_nice_tries+2);
 }
 
@@ -7881,7 +7888,8 @@ static int idle_balance(struct rq *this_rq)
 	this_rq->idle_stamp = rq_clock(this_rq);
 
 	if (this_rq->avg_idle < sysctl_sched_migration_cost ||
-	    !this_rq->rd->overload) {
+	    (!energy_aware() && !this_rq->rd->overload) ||
+	    (energy_aware() && !this_rq->rd->overutilized)) {
 		rcu_read_lock();
 		sd = rcu_dereference_check_sched_domain(this_rq->sd);
 		if (sd)
-- 
1.9.1

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