linux-kernel - [tip:sched/core] sched: Optimize branch hint in context

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Message-ID: <tip-710390d90f143a9ebb87a475215140f426792efd@git.kernel.org>
Date:	Tue, 24 Nov 2009 16:56:51 GMT
From:	tip-bot for Tim Blechmann <tim@...ngt.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, paulus@...ba.org,
	hpa@...or.com, mingo@...hat.com, a.p.zijlstra@...llo.nl,
	efault@....de, fweisbec@...il.com, tglx@...utronix.de,
	tim@...ngt.org, mingo@...e.hu
Subject: [tip:sched/core] sched: Optimize branch hint in context_switch()

Commit-ID:  710390d90f143a9ebb87a475215140f426792efd
Gitweb:     http://git.kernel.org/tip/710390d90f143a9ebb87a475215140f426792efd
Author:     Tim Blechmann <tim@...ngt.org>
AuthorDate: Tue, 24 Nov 2009 11:55:27 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 24 Nov 2009 12:18:42 +0100

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 <tim@...ngt.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Mike Galbraith <efault@....de>
Cc: Paul Mackerras <paulus@...ba.org>
Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
Cc: Frederic Weisbecker <fweisbec@...il.com>
LKML-Reference: <4B0BBB9F.6080304@...ngt.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 93474a7..010d5e1 100644
--- 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;
 	}
--
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