linux-kernel - Re: Linux 2.6.32-rc1

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Message-ID: <20090929232248.735bf4df@infradead.org>
Date:	Tue, 29 Sep 2009 23:22:48 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Linux 2.6.32-rc1

On Tue, 29 Sep 2009 14:17:58 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Tue, 29 Sep 2009, Eric Dumazet wrote:
> > 
> > Checking this commit, I believe problem comes from cmpxchg(), which
> > doesnt handle 64 bit on X86_32 (no compilation error, and  null
> > operation :( )
> 
> Wow. That's broken. Very nasty silent failure.
> 
> > 1) Use cmpxchg64()
> 
> Clearly better than what we have now, although cmpxchg64 does result
> is some really disgusting code. We will use a bare CMPXCHG64 only if
> you compile for PAE right now - so even if you tell Kconfig that you
> want to compile for a modern CPU, we won't be doing that whole
> cmpxchg64b thing directly, we'll inline some really disgusting code.

can't we use alternatives() for this, to patch cmpxchg64 in ?
I mean.. it'll be commonly supported nowadays.. the fallback to it not
being supported could be a bit slower by now...


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
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