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i386: add cpu_relax() to cmos_lock()

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Add cpu_relax() to cmos_lock() inline function for faster operation on SMT
CPUs and less power consumption on others in case of lock contention (which
probably doesn't happen too often, so admittedly this patch is not too
exciting).

[akpm@linux-foundation.org: Include the header file for cpu_relax()]
Signed-off-by: Andreas Mohr <andi@lisas.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andreas Mohr 2007-07-21 17:11:25 +02:00 committed by Linus Torvalds
parent 8f03d6ce4e
commit 267eb01a62
1 changed files with 4 additions and 1 deletions
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5
include/asm-i386/mc146818rtc.h
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@ -6,6 +6,7 @@
#include <asm/io.h>
#include <asm/system.h>
#include <asm/processor.h>
#include <linux/mc146818rtc.h>
#ifndef RTC_PORT
@ -43,8 +44,10 @@ static inline void lock_cmos(unsigned char reg)
unsigned long new;
new = ((smp_processor_id()+1) << 8) | reg;
for (;;) {
if (cmos_lock)
if (cmos_lock) {
cpu_relax();
continue;
}
if (__cmpxchg(&cmos_lock, 0, new, sizeof(cmos_lock)) == 0)
return;
}