linux-kernel - [PATCH] sched: Get rid of unnecessary checks from select_idle

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Date:	Wed,  9 Jan 2013 15:50:56 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Mike Galbraith <efault@....de>,
	Preeti U Murthy <preeti@...ux.vnet.ibm.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Alex Shi <alex.shi@...el.com>
Subject: [PATCH] sched: Get rid of unnecessary checks from select_idle_sibling

From: Namhyung Kim <namhyung.kim@....com>

AFAICS @target cpu of select_idle_sibling() is always either prev_cpu
or this_cpu.  So no need to check it again and the conditionals can be
consolidated.

Cc: Mike Galbraith <efault@....de>
Cc: Preeti U Murthy <preeti@...ux.vnet.ibm.com>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
Cc: Alex Shi <alex.shi@...el.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 kernel/sched/fair.c | 17 ++++-------------
 1 file changed, 4 insertions(+), 13 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5eea8707234a..af665814c216 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3254,25 +3254,16 @@ find_idlest_cpu(struct sched_group *group, struct task_struct *p, int this_cpu)
  */
 static int select_idle_sibling(struct task_struct *p, int target)
 {
-	int cpu = smp_processor_id();
-	int prev_cpu = task_cpu(p);
 	struct sched_domain *sd;
 	struct sched_group *sg;
 	int i;
 
 	/*
-	 * If the task is going to be woken-up on this cpu and if it is
-	 * already idle, then it is the right target.
-	 */
-	if (target == cpu && idle_cpu(cpu))
-		return cpu;
-
-	/*
-	 * If the task is going to be woken-up on the cpu where it previously
-	 * ran and if it is currently idle, then it the right target.
+	 * If the task is going to be woken-up on this cpu or the cpu where it
+	 * previously ran and it is already idle, then it is the right target.
 	 */
-	if (target == prev_cpu && idle_cpu(prev_cpu))
-		return prev_cpu;
+	if (idle_cpu(target))
+		return target;
 
 	/*
 	 * Otherwise, iterate the domains and find an elegible idle cpu.
-- 
1.7.11.7

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