linux-kernel - [tip:sched/core] printk: Use this_cpu_{read|write} api on printk

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Date:	Wed, 8 Dec 2010 20:41:52 GMT
From:	tip-bot for Eric Dumazet <eric.dumazet@...il.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	eric.dumazet@...il.com, a.p.zijlstra@...llo.nl, cl@...ux.com,
	heiko.carstens@...ibm.com, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/core] printk: Use this_cpu_{read|write} api on printk_pending

Commit-ID:  40dc11ffb35e8c4e8fa71092048e0f8de9db758c
Gitweb:     http://git.kernel.org/tip/40dc11ffb35e8c4e8fa71092048e0f8de9db758c
Author:     Eric Dumazet <eric.dumazet@...il.com>
AuthorDate: Fri, 26 Nov 2010 17:22:16 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 8 Dec 2010 20:16:01 +0100

printk: Use this_cpu_{read|write} api on printk_pending

__get_cpu_var() is a bit inefficient, lets use __this_cpu_read() and
__this_cpu_write() to manipulate printk_pending.

printk_needs_cpu(cpu) is called only for the current cpu :
Use faster __this_cpu_read().

Remove the redundant unlikely on (cpu_is_offline(cpu)) test:

 # size kernel/printk.o*
   text	   data	    bss	    dec	    hex	filename
   9942	    756	 263488	 274186	  42f0a	kernel/printk.o.new
   9990	    756	 263488	 274234	  42f3a	kernel/printk.o.old

Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Christoph Lameter <cl@...ux.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1290788536.2855.237.camel@...mazet-laptop>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/printk.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/printk.c b/kernel/printk.c
index a23315d..ab3ffc5 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1074,17 +1074,17 @@ static DEFINE_PER_CPU(int, printk_pending);
 
 void printk_tick(void)
 {
-	if (__get_cpu_var(printk_pending)) {
-		__get_cpu_var(printk_pending) = 0;
+	if (__this_cpu_read(printk_pending)) {
+		__this_cpu_write(printk_pending, 0);
 		wake_up_interruptible(&log_wait);
 	}
 }
 
 int printk_needs_cpu(int cpu)
 {
-	if (unlikely(cpu_is_offline(cpu)))
+	if (cpu_is_offline(cpu))
 		printk_tick();
-	return per_cpu(printk_pending, cpu);
+	return __this_cpu_read(printk_pending);
 }
 
 void wake_up_klogd(void)
--
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