linux-kernel - [RFC PATCH] sched: select_idle

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Date:	Wed, 15 Jan 2014 22:23:28 +0800
From:	Alex Shi <alex.shi@...aro.org>
To:	mingo@...hat.com, peterz@...radead.org, morten.rasmussen@....com,
	vincent.guittot@...aro.org, daniel.lezcano@...aro.org
Cc:	wangyun@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	Alex Shi <alex.shi@...aro.org>
Subject: [RFC PATCH] sched: select_idle_sibling macro optimize

If the sd domain just has one group, then we must be caught the
	i == target later, and then goes to deeper level domain.
So just skip this domain checking to save some instructions.

Signed-off-by: Alex Shi <alex.shi@...aro.org>
---
 kernel/sched/fair.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c7395d9..3265fbc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4196,6 +4196,11 @@ static int select_idle_sibling(struct task_struct *p, int target)
 	sd = rcu_dereference(per_cpu(sd_llc, target));
 	for_each_lower_domain(sd) {
 		sg = sd->groups;
+
+		/* skip single group domain */
+		if (sg == sg->next)
+			continue;
+
 		do {
 			if (!cpumask_intersects(sched_group_cpus(sg),
 						tsk_cpus_allowed(p)))
-- 
1.8.1.2

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