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

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Message-ID: <20090703184353.GB4085@elte.hu>
Date:	Fri, 3 Jul 2009 20:43:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
Cc:	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> wrote:

> On Fri, 3 Jul 2009 20:18:15 +0200
> Ingo Molnar <mingo@...e.hu> wrote:
> 
> > 
> > * Arjan van de Ven <arjan@...radead.org> wrote:
> > 
> > > 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
> > 
> > good point!
> > 
> > Is the same true of XADD as well? If yes then we can remove the lock 
> > prefix from those as well - there's a few uses of that on 32-bit and 
> > 64-bit as well.
> > 
> 
> ok never mind I was wrong,
> it seems cmpxchg does NOT imply a lock prefix, nor does xadd.

Indeed, i just checked the SDM and the lock prefix is not implicit.

Ignore the patch i sent out ;-)

	Ingo
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