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>

1 files changed, 6 insertions, 2 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index e717047be5c..4f13d379bea 100644
--- 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) &&