linux-kernel - [tip:smp/hotplug] smpboot, idle: Optimize calls to smp_processor_id() in idle_threads

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Message-ID: <tip-ee74d13229fb606353ff56f4927fa93b37e95bbe@git.kernel.org>
Date:	Thu, 24 May 2012 14:04:28 -0700
From:	"tip-bot for Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	srivatsa.bhat@...ux.vnet.ibm.com, tglx@...utronix.de
Subject: [tip:smp/hotplug] smpboot, idle:
  Optimize calls to smp_processor_id() in idle_threads_init()

Commit-ID:  ee74d13229fb606353ff56f4927fa93b37e95bbe
Gitweb:     http://git.kernel.org/tip/ee74d13229fb606353ff56f4927fa93b37e95bbe
Author:     Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
AuthorDate: Thu, 24 May 2012 20:40:55 +0530
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Thu, 24 May 2012 22:58:08 +0200

smpboot, idle: Optimize calls to smp_processor_id() in idle_threads_init()

While trying to initialize idle threads for all cpus, idle_threads_init()
calls smp_processor_id() in a loop, which is unnecessary. The intent
is to initialize idle threads for all non-boot cpus. So just use a variable
to note the boot cpu and use it in the loop.

Signed-off-by: Srivatsa S. Bhat <srivatsa.bhat@...ux.vnet.ibm.com>
Cc: suresh.b.siddha@...el.com
Cc: venki@...gle.com
Cc: nikunj@...ux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20120524151055.2549.64309.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/smpboot.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index e1a797e..0f2162f 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -52,10 +52,12 @@ static inline void idle_init(unsigned int cpu)
  */
 void __init idle_threads_init(void)
 {
-	unsigned int cpu;
+	unsigned int cpu, boot_cpu;
+
+	boot_cpu = smp_processor_id();
 
 	for_each_possible_cpu(cpu) {
-		if (cpu != smp_processor_id())
+		if (cpu != boot_cpu)
 			idle_init(cpu);
 	}
 }
--
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