sched: Optimize branch hint in context_switch()

Branch hint profiling on my nehalem machine showed over 90%
incorrect branch hints:

  10420275 170645395  94 context_switch                 sched.c
   3043
  10408421 171098521  94 context_switch                 sched.c
   3050

Signed-off-by: Tim Blechmann <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
LKML-Reference: <4B0BBB9F.6080304@klingt.org>
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/sched.c b/kernel/sched.c
index 93474a7935ae482aaa4fdd2d99f37a2830b00fe1..010d5e16b4c5efe56976d01c1190f2deb25f5f3a 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2829,14 +2829,14 @@ context_switch(struct rq *rq, struct task_struct *prev,
         */
        arch_start_context_switch(prev);
 
-       if (unlikely(!mm)) {
+       if (likely(!mm)) {
                next->active_mm = oldmm;
                atomic_inc(&oldmm->mm_count);
                enter_lazy_tlb(oldmm, next);
        } else
                switch_mm(oldmm, mm, next);
 
-       if (unlikely(!prev->mm)) {
+       if (likely(!prev->mm)) {
                prev->active_mm = NULL;
                rq->prev_mm = oldmm;
        }