linux-kernel - [PATCH V2 8/8] sched: don't queue timers on quiesced CPUs

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Date:	Fri,  4 Apr 2014 14:05:35 +0530
From:	Viresh Kumar <viresh.kumar@...aro.org>
To:	tglx@...utronix.de, fweisbec@...il.com, peterz@...radead.org,
	mingo@...nel.org, tj@...nel.org, lizefan@...wei.com
Cc:	linaro-kernel@...ts.linaro.org, linaro-networking@...aro.org,
	Arvind.Chauhan@....com, linux-kernel@...r.kernel.org,
	cgroups@...r.kernel.org, Viresh Kumar <viresh.kumar@...aro.org>
Subject: [PATCH V2 8/8] sched: don't queue timers on quiesced CPUs

CPUSets have cpusets.quiesce sysfs file now, with which some CPUs can opt for
isolating themselves from background kernel activities, like: timers & hrtimers.

get_nohz_timer_target() is used for finding suitable CPU for firing a timer. To
guarantee that new timers wouldn't be queued on quiesced CPUs, we need to modify
this routine.

Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
---
 kernel/sched/core.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index c0339e2..b235af2 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -557,17 +557,18 @@ void resched_cpu(int cpu)
  */
 int get_nohz_timer_target(int pinned)
 {
-	int cpu = smp_processor_id();
-	int i;
+	int cpu = smp_processor_id(), i;
 	struct sched_domain *sd;
 
-	if (pinned || !get_sysctl_timer_migration() || !idle_cpu(cpu))
+	if (pinned || !get_sysctl_timer_migration() ||
+	    !(idle_cpu(cpu) || cpu_quiesced(cpu)))
 		return cpu;
 
 	rcu_read_lock();
 	for_each_domain(cpu, sd) {
 		for_each_cpu(i, sched_domain_span(sd)) {
-			if (!idle_cpu(i)) {
+			/* Don't push timers to quiesced CPUs */
+			if (!(cpu_quiesced(i) || idle_cpu(i))) {
 				cpu = i;
 				goto unlock;
 			}
-- 
1.7.12.rc2.18.g61b472e

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