linux-kernel - Re: [PATCH -tip] x86: atomic64: inline atomic64

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Message-ID: <87ocs1aall.fsf@basil.nowhere.org>
Date:	Fri, 03 Jul 2009 20:24:22 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Eric Dumazet <eric.dumazet@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -tip] x86: atomic64: inline atomic64_read()

Arjan van de Ven <arjan@...radead.org> writes:

> On Fri, 3 Jul 2009 20:04:50 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
>
>> > +static inline u64 atomic64_read(atomic64_t *ptr)
>> > +{
>> > +	u64 res;
>> > +
>> > +	asm volatile(
>> > +		"mov %%ebx, %%eax\n\t"
>> > +		"mov %%ecx, %%edx\n\t"
>> > +		LOCK_PREFIX "cmpxchg8b %1\n"
>
> also afaik cmpxchg implies the lock prefix, so no need to make an
> explicit one... it just adds code size and alternatives-work

No it doesn't; LOCK is implied for "xchg", but not for cmpxchg

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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