linux-kernel - Re: [PATCH 00/18] x86: Ticket lock + cmpxchg cleanup

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Message-ID: <CA+55aFy2E+t2oNGPe1nx4nRXMiFaq29h6F1x8H+sVDoHDiryZQ@mail.gmail.com>
Date:	Wed, 24 Aug 2011 16:21:17 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 00/18] x86: Ticket lock + cmpxchg cleanup

On Wed, Aug 24, 2011 at 4:09 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> However, the reason I disagree with it is that I don't think that it's
> any prettier at all to have the two barriers than it is to just have
> the asm.

.. and btw, we probably do need *both* barriers. We definitely need
the one before. The one after is a bit less obvious, since it is
technically legal for code to move into the locked region. However,
it's not necessarily a *good* idea for code to move into the locked
region, so the two barriers are likely the RightThing(tm). But the two
barriers are what makes me think that the C version really isn't any
better. And the OOSTORE case then just clinches the deal for me.

                         Linus
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