linux-kernel - [tip:sched/core] sched: Fix nohz_idle

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Date:	Thu, 13 Sep 2012 23:12:17 -0700
From:	tip-bot for Vincent Guittot <vincent.guittot@...aro.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	a.p.zijlstra@...llo.nl, vincent.guittot@...aro.org,
	suresh.b.siddha@...el.com, tglx@...utronix.de, venki@...gle.com
Subject: [tip:sched/core] sched: Fix nohz_idle_balance()

Commit-ID:  5ed4f1d96deee82ee92cd1ac1e0108c27e80e9b0
Gitweb:     http://git.kernel.org/tip/5ed4f1d96deee82ee92cd1ac1e0108c27e80e9b0
Author:     Vincent Guittot <vincent.guittot@...aro.org>
AuthorDate: Thu, 13 Sep 2012 06:11:26 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 13 Sep 2012 16:52:03 +0200

sched: Fix nohz_idle_balance()

On tickless systems, one CPU runs load balance for all idle CPUs.

The cpu_load of this CPU is updated before starting the load balance
of each other idle CPUs. We should instead update the cpu_load of
the balance_cpu.

Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Venkatesh Pallipadi <venki@...gle.com>
Cc: Suresh Siddha <suresh.b.siddha@...el.com>
Link: http://lkml.kernel.org/r/1347509486-8688-1-git-send-email-vincent.guittot@linaro.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c |   11 ++++++-----
 1 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1ca4fe4..9ae3a5b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4794,14 +4794,15 @@ static void nohz_idle_balance(int this_cpu, enum cpu_idle_type idle)
 		if (need_resched())
 			break;
 
-		raw_spin_lock_irq(&this_rq->lock);
-		update_rq_clock(this_rq);
-		update_idle_cpu_load(this_rq);
-		raw_spin_unlock_irq(&this_rq->lock);
+		rq = cpu_rq(balance_cpu);
+
+		raw_spin_lock_irq(&rq->lock);
+		update_rq_clock(rq);
+		update_idle_cpu_load(rq);
+		raw_spin_unlock_irq(&rq->lock);
 
 		rebalance_domains(balance_cpu, CPU_IDLE);
 
-		rq = cpu_rq(balance_cpu);
 		if (time_after(this_rq->next_balance, rq->next_balance))
 			this_rq->next_balance = rq->next_balance;
 	}
--
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