linux-kernel - [tip:sched/core] sched, nohz: Exclude isolated cores from load balancing

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Date:	Sat, 22 Feb 2014 10:04:42 -0800
From:	tip-bot for Mike Galbraith <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, mgalbraith@...e.de, hpa@...or.com,
	mingo@...nel.org, leiwen@...vell.com, peterz@...radead.org,
	tglx@...utronix.de
Subject: [tip:sched/core] sched, nohz:
  Exclude isolated cores from load balancing

Commit-ID:  d987fc7f3228bf94cb6b21313ebab1d64ee637ad
Gitweb:     http://git.kernel.org/tip/d987fc7f3228bf94cb6b21313ebab1d64ee637ad
Author:     Mike Galbraith <mgalbraith@...e.de>
AuthorDate: Mon, 5 Dec 2011 10:01:47 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Sat, 22 Feb 2014 18:17:22 +0100

sched, nohz: Exclude isolated cores from load balancing

The user explicitly disabled load balancing, else this core would not be
disconnected.  Don't add these to nohz.idle_cpus_mask.

Signed-off-by: Mike Galbraith <mgalbraith@...e.de>
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Cc: Lei Wen <leiwen@...vell.com>
Link: http://lkml.kernel.org/n/tip-vmme4f49psirp966pklm5l9j@git.kernel.org
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/fair.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7982faf..a3a41c61 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6788,6 +6788,11 @@ out_unlock:
 	return 0;
 }
 
+static inline int on_null_domain(struct rq *rq)
+{
+	return unlikely(!rcu_dereference_sched(rq->sd));
+}
+
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * idle load balancing details
@@ -6842,8 +6847,13 @@ static void nohz_balancer_kick(void)
 static inline void nohz_balance_exit_idle(int cpu)
 {
 	if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
-		cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
-		atomic_dec(&nohz.nr_cpus);
+		/*
+		 * Completely isolated CPUs don't ever set, so we must test.
+		 */
+		if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
+			cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
+			atomic_dec(&nohz.nr_cpus);
+		}
 		clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
 	}
 }
@@ -6897,6 +6907,12 @@ void nohz_balance_enter_idle(int cpu)
 	if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
 		return;
 
+	/*
+	 * If we're a completely isolated CPU, we don't play.
+	 */
+	if (on_null_domain(cpu_rq(cpu)))
+		return;
+
 	cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
 	atomic_inc(&nohz.nr_cpus);
 	set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
@@ -7159,11 +7175,6 @@ static void run_rebalance_domains(struct softirq_action *h)
 	nohz_idle_balance(this_rq, idle);
 }
 
-static inline int on_null_domain(struct rq *rq)
-{
-	return !rcu_dereference_sched(rq->sd);
-}
-
 /*
  * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
  */
--
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