linux-kernel - Re: [PATCH 09/10] x86-32: use SSE for atomic64

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Message-ID: <4B7D7060.1080908@zytor.com>
Date:	Thu, 18 Feb 2010 08:52:48 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Luca Barbieri <luca@...a-barbieri.com>
CC:	Andi Kleen <andi@...stfloor.org>, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 09/10] x86-32: use SSE for atomic64_read/set if available

On 02/18/2010 02:27 AM, Luca Barbieri wrote:
>> So why don't you simply use normal asm inputs/outputs?
> I do, on the caller side.
> 
> In the callee, I don't see any other robust way to implement parameter
> passing in ebx/esi other than global register variables (without
> resorting to pure assembly, which would prevent reusing the generic
> atomic64 implementation).

This really sounds like the wrong optimization.  These functions aren't
exactly all that complex in assembly (which would also allow them to be
simple cli/do stuff/sti), and instead relying on gcc features which may
or may not be well supported on x86 is inviting breakage down the line.

That is particularly damaging, since the remaining 486-class users tend
to be deeply embedded and thus we only find problems later.

	-hpa
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