linux-kernel - Re: [tip:core/locking] x86/smp: Move waiting on contended ticket lock out of line

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Message-ID: <511C444F.1040707@zytor.com>
Date:	Wed, 13 Feb 2013 17:56:31 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>, rostedt@...dmiss.org,
	aquini@...hat.com, Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Michel Lespinasse <walken@...gle.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:core/locking] x86/smp: Move waiting on contended ticket
 lock out of line

On 02/13/2013 05:31 PM, Linus Torvalds wrote:
> On Wed, Feb 13, 2013 at 4:54 PM, H. Peter Anvin <hpa@...or.com> wrote:
>>
>> It does for the callee, but only on a whole-file basis.  It would be a
>> lot nicer if we could do it with function attributes.
> 
> A way to just set the callee-clobbered list on a per-function basis
> would be lovely. Gcc has limited support for this on some
> architectures, where you can specify "save every register for this
> function" in order to do things like interrupt handlers etc without
> even resorting to asm. But there is no generic (or even just x86)
> support for anything like it :-(
> 
> There are other calling-convention attributes that make me suspect gcc
> could easily do this (it already supports per-function ABI
> specification, so presumably it already has some concept of
> callee-saved registers being different for different attributes), but
> from my reading you currently have to generate asm wrappers by hand
> (and call them by hand with inline asm) if you want to do something
> like this.
> 

I just filed a gcc bugzilla on this:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56314

	-hpa

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