linux-kernel - Re: [tip:sched/urgent] x86: Provide an alternative() based cmpxchg64()

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Message-ID: <20090930205808.GC24862@elte.hu>
Date:	Wed, 30 Sep 2009 22:58:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, arjan@...ux.intel.com,
	torvalds@...ux-foundation.org, johnstul@...ibm.com,
	a.p.zijlstra@...llo.nl, schwidefsky@...ibm.com,
	arjan@...radead.org, tglx@...utronix.de
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/urgent] x86: Provide an alternative() based
	cmpxchg64()


* tip-bot for Arjan van de Ven <arjan@...radead.org> wrote:

> Commit-ID:  e87aaa7b6d80474ec07a2d2be3f50ef574ffe36c
> Gitweb:     http://git.kernel.org/tip/e87aaa7b6d80474ec07a2d2be3f50ef574ffe36c
> Author:     Arjan van de Ven <arjan@...radead.org>
> AuthorDate: Wed, 30 Sep 2009 17:07:54 +0200
> Committer:  Ingo Molnar <mingo@...e.hu>
> CommitDate: Wed, 30 Sep 2009 22:35:44 +0200
> 
> x86: Provide an alternative() based cmpxchg64()
> 
> cmpxchg64() today generates, to quote Linus, "barf bag" code.
> 
> cmpxchg64() is about to get used in the scheduler to a bug there,
> but it's a prerequisite that cmpxchg64() first be made non-sucking.
> 
> This patch turns cmpxchg64() into an efficient implementation that
> uses the alternative() mechanism to just use the raw instruction on
> all modern systens

The changelog above has 3 typos so i fixed that. The push will generate 
the hopefully-final version of these patches.

Note, i slightly updated Linus's version of the old-CPU emu code with 
Eric's micro-optimization.

	Ingo
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