linux-kernel - [tip:sched/core] sched, x86: Optimize branch hint in __switch

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Date:	Tue, 24 Nov 2009 16:57:05 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, x86: Optimize branch hint in __switch_to()

Commit-ID:  a3a1de0c34de6f5f8332cd6151c46af7813c0fcb
Gitweb:     http://git.kernel.org/tip/a3a1de0c34de6f5f8332cd6151c46af7813c0fcb
Author:     Tim Blechmann <tim@...ngt.org>
AuthorDate: Tue, 24 Nov 2009 11:55:15 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 24 Nov 2009 12:20:04 +0100

sched, x86: Optimize branch hint in __switch_to()

Branch hint profiling on my nehalem machine showed 96%
incorrect branch hints:

  6548732 174664120  96 __switch_to                    process_64.c
    406
  6548745 174565593  96 __switch_to                    process_64.c
    410

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: <4B0BBB93.3080307@...ngt.org>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/kernel/process_64.c |    5 ++---
 1 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index ad535b6..d9db104 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -406,11 +406,10 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
 	 * This won't pick up thread selector changes, but I guess that is ok.
 	 */
 	savesegment(es, prev->es);
-	if (unlikely(next->es | prev->es))
+	if (next->es | prev->es)
 		loadsegment(es, next->es);
-
 	savesegment(ds, prev->ds);
-	if (unlikely(next->ds | prev->ds))
+	if (next->ds | prev->ds)
 		loadsegment(ds, next->ds);
 
 
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