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

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Date:	Thu, 18 Feb 2010 11:06:13 -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 10:49 AM, Luca Barbieri wrote:
>> 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.
> 
> There is the downside of adding a whole 386/486-specific implementation.
> 
> It's not too hard though, and if we don't care about 486 SMP, it may
> be a better option.

We don't care about 486 SMP.  And yes, I think it is a better option.
At least an assembly option, once implemented, will *stay* implemented
and won't break due to some obscure gcc change.

	-hpa

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