sched: optimize schedule() a bit on SMP

optimize schedule() a bit on SMP, by moving the rq-clock update
outside the rq lock.

code size is the same:

      text    data     bss     dec     hex filename
     25725    2666      96   28487    6f47 sched.o.before
     25725    2666      96   28487    6f47 sched.o.after
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Reviewed-by: NThomas Gleixner <tglx@linutronix.de>

kernel/sched.c

@@ -3481,9 +3481,13 @@ asmlinkage void __sched schedule(void)
 
 	schedule_debug(prev);
 
-	spin_lock_irq(&rq->lock);
-	clear_tsk_need_resched(prev);
+	/*
+	 * Do the rq-clock update outside the rq lock:
+	 */
+	local_irq_disable();
 	__update_rq_clock(rq);
+	spin_lock(&rq->lock);
+	clear_tsk_need_resched(prev);
 
 	if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
 		if (unlikely((prev->state & TASK_INTERRUPTIBLE) &&