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: Ingo Molnar <mingo@elte.hu>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/sched.c b/kernel/sched.c
index e717047..4f13d37 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3481,9 +3481,13 @@ need_resched_nonpreemptible:
 
        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) &&