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

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Message-ID: <4E5583B3.8080309@zytor.com>
Date:	Wed, 24 Aug 2011 16:05:23 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.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 08/24/2011 03:59 PM, Jeremy Fitzhardinge wrote:
> On 08/24/2011 03:53 PM, Linus Torvalds wrote:
>> On Wed, Aug 24, 2011 at 1:10 PM, Jeremy Fitzhardinge <jeremy@...p.org> wrote:
>>> Could we just kill SMP support for OOSTORE machines now?  That would be
>>> the cleanest possible fix...
>> No it wouldn't. The asm version would *still* be cleaner than the "C
>> plus random barriers".
>>
>> It's not like the C version is "portable" in any case.
> 
> If there's no need to have a locked instruction, then it could simply be:
> 
>     barrier();
>     lock->head++;
>     barrier();
> 
> with no need for asm at all.
> 

That's not guaranteed in any way to generate a locally atomic instruction.

	-hpa


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