linux-kernel - [PATCH 1/2] smpboot, idle: Optimize calls to smp_processor_id() in idle_threads

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Message-ID: <20120524151055.2549.64309.stgit@srivatsabhat.in.ibm.com>
Date:	Thu, 24 May 2012 20:40:55 +0530
From:	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>
To:	tglx@...utronix.de
Cc:	suresh.b.siddha@...el.com, venki@...gle.com,
	nikunj@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] 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>
---

 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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