[PATCH v2 03/13] sched/fair: Optimize find_idlest_cpu() when there is no choice

From: Morten Rasmussen <morten.rasmussen@arm.com>
To: peterz@infradead.org, mingo@redhat.com
Cc: dietmar.eggemann@arm.com, yuyang.du@intel.com,
	vincent.guittot@linaro.org, mgalbraith@suse.de,
	linux-kernel@vger.kernel.org,
	Morten Rasmussen <morten.rasmussen@arm.com>
Subject: [PATCH v2 03/13] sched/fair: Optimize find_idlest_cpu() when there is no choice
Date: Wed, 22 Jun 2016 18:03:14 +0100	[thread overview]
Message-ID: <1466615004-3503-4-git-send-email-morten.rasmussen@arm.com> (raw)
In-Reply-To: <1466615004-3503-1-git-send-email-morten.rasmussen@arm.com>

In the current find_idlest_group()/find_idlest_cpu() search we end up
calling find_idlest_cpu() in a sched_group containing only one cpu in
the end. Checking idle-states becomes pointless when there is no
alternative, so bail out instead.

cc: Ingo Molnar <mingo@redhat.com>
cc: Peter Zijlstra <peterz@infradead.org>

Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
---
 kernel/sched/fair.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index eec8e29104f9..216db302e87d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5123,6 +5123,10 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
 	int shallowest_idle_cpu = -1;
 	int i;
 
+	/* Check if we have any choice */
+	if (group->group_weight == 1)
+		return cpumask_first(sched_group_cpus(group));
+
 	/* Traverse only the allowed CPUs */
 	for_each_cpu_and(i, sched_group_cpus(group), tsk_cpus_allowed(p)) {
 		if (idle_cpu(i)) {
-- 
1.9.1
