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@linux.vnet.ibm.com>
Cc: suresh.b.siddha@intel.com
Cc: venki@google.com
Cc: nikunj@linux.vnet.ibm.com
Link: http://lkml.kernel.org/r/20120524151055.2549.64309.stgit@srivatsabhat.in.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

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);
 	}
 }