[PATCH v3 03/13] sched/fair: Optimize find_idlest_cpu() when there is no choice

From: Morten Rasmussen
Date: Mon Jul 25 2016 - 09:35:20 EST


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@xxxxxxxxxx>
cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>

Acked-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Signed-off-by: Morten Rasmussen <morten.rasmussen@xxxxxxx>
---
kernel/sched/fair.c | 4 ++++
1 file changed, 4 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e7d50acd6028..c1c0aa8b300b 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5229,6 +5229,10 @@ 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