linux-kernel - [PATCH] sched: keep quiescent cpu out of idle balance loop

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Message-ID: <1392787230-17986-1-git-send-email-leiwen@marvell.com>
Date:	Wed, 19 Feb 2014 13:20:30 +0800
From:	Lei Wen <leiwen@...vell.com>
To:	<peterz@...radead.org>, <mingo@...hat.com>,
	<preeti.lkml@...il.com>, <daniel.lezcano@...aro.org>,
	<viresh.kumar@...aro.org>, <xjian@...vell.com>,
	<leiwen@...vell.com>, <linux-kernel@...r.kernel.org>
Subject: [PATCH] sched: keep quiescent cpu out of idle balance loop

Since cpu which is put into quiescent mode, would remove itself
from kernel's sched_domain. So we could use search sched_domain
method to check whether this cpu don't want to be disturbed as
idle load balance would send IPI to it.

Signed-off-by: Lei Wen <leiwen@...vell.com>
---
 kernel/sched/fair.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 235cfa7..14230ae 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6783,6 +6783,8 @@ out_unlock:
  * - When one of the busy CPUs notice that there may be an idle rebalancing
  *   needed, they will kick the idle load balancer, which then does idle
  *   load balancing for all the idle CPUs.
+ * - exclude those cpus not inside current call_cpu's sched_domain, so that
+ *   those isolated cpu could be kept in their quisecnt mode.
  */
 static struct {
 	cpumask_var_t idle_cpus_mask;
@@ -6792,10 +6794,16 @@ static struct {
 
 static inline int find_new_ilb(void)
 {
-	int ilb = cpumask_first(nohz.idle_cpus_mask);
+	int ilb;
+	int cpu = smp_processor_id();
+	struct sched_domain *tmp;
 
-	if (ilb < nr_cpu_ids && idle_cpu(ilb))
-		return ilb;
+	for_each_domain(cpu, tmp) {
+		ilb = cpumask_first_and(nohz.idle_cpus_mask,
+				sched_domain_span(tmp));
+		if (ilb < nr_cpu_ids && idle_cpu(ilb))
+			return ilb;
+	}
 
 	return nr_cpu_ids;
 }
-- 
1.8.3.2

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