linux-kernel - Re: [GIT PULL] x86/atomic changes for v2.6.35

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Message-ID: <4BF3F480.3000902@zytor.com>
Date:	Wed, 19 May 2010 07:24:00 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Ingo Molnar <mingo@...e.hu>,
	Luca Barbieri <luca@...a-barbieri.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-arch@...r.kernel.org
Subject: Re: [GIT PULL] x86/atomic changes for v2.6.35

On 05/19/2010 04:46 AM, Geert Uytterhoeven wrote:
> On Tue, May 18, 2010 at 00:45, Ingo Molnar <mingo@...e.hu> wrote:
>> Please pull the latest x86-atomic-for-linus git tree from:
>>
>>   git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip.git x86-atomic-for-linus
>>
>>
>> out-of-topic modifications in x86-atomic-for-linus:
>> ---------------------------------------------------
>> lib/Makefile                       # 86a8938: lib: Add self-test for atomic64_t
>> lib/atomic64.c                     # 9757789: lib: Fix atomic64_add_unless retu
>> lib/atomic64_test.c                # a5c9161: x86, atomic64: In selftest, disti
>>                                   # 25a304f: lib: Fix atomic64_inc_not_zero te
>>                                   # 9efbcd5: lib: Fix atomic64_add_unless test
>>                                   # d7f6de1: x86: Implement atomic[64]_dec_if_
>>                                   # 8f4f202: lib: Only test atomic64_dec_if_po
>>                                   # 86a8938: lib: Add self-test for atomic64_t
> 
> Is having atomic64_t mandatory now?
> 
> According to the allmodconfig build logs
> (http://kisskb.ellerman.id.au/kisskb/matrix/),
> several architectures (at least m68k and mips) don't have it.
> Furthermore, the test fails to compile on a few architectures that do have it
> (parisc, s390, sh, ...).
> 
> <boilerplate>
> It's a pity this wasn't raised/resolved between its detection in linux-next and
> before it entered mainline...
> </boilerplate>
> 

Is having atomic64_t mandatory?  Not yet, I don't think, but it probably
will be soon -- which is why there is a generic implementation
available.  All those architectures just need to select
CONFIG_GENERIC_ATOMIC64 and voilà, problem solved.

As far as your boilerplate is concerned, I think Linus made it clear at
the Kernel Summit that is it not the obligation of x86/ARM/PowerPC to
slow down to not break the smaller architectures; it's the
responsibility of those architecture maintainers to keep up.  Sorry.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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