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x86: wmb() confusion in system.h

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Comment says wmb is a nop, but it is implemented as lock addl
below... Should it be compiled to nop if we know we are running on
"good" Intel cpu?

At least remove confusing comment for now.

Signed-off-by: Pavel Machek <pavel@suse.cz>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Pavel Machek 2008-03-03 12:49:09 +01:00 committed by Ingo Molnar
parent 3c2047cd32
commit 0d7a1819e9
1 changed files with 1 additions and 10 deletions
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11
include/asm-x86/system.h
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@ -296,16 +296,7 @@ void default_idle(void);
*/
#ifdef CONFIG_X86_32
/*
* For now, "wmb()" doesn't actually do anything, as all
* Intel CPU's follow what Intel calls a *Processor Order*,
* in which all writes are seen in the program order even
* outside the CPU.
*
* I expect future Intel CPU's to have a weaker ordering,
* but I'd also expect them to finally get their act together
* and add some real memory barriers if so.
*
* Some non intel clones support out of order store. wmb() ceases to be a
* Some non-Intel clones support out of order store. wmb() ceases to be a
* nop for these.
*/
#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)