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

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Message-ID: <4B7D8FE0.1040602@zytor.com>
Date:	Thu, 18 Feb 2010 11:07:12 -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 10:42 AM, Luca Barbieri wrote:
>> We already do that kind of stuff, using
>> kernel_fpu_begin()..kernel_fpu_end().  We went through some pain a bit
>> ago to clean up "private hacks" that complicated things substantially.
> 
> But that saves the whole FPU state on the first usage, and also
> triggers a fault when userspace attempts to use it again.
> Additionally it does a clts/stts every time which is slow for small
> algorithms (lke the atomic64 routines).
> 
> The first issue can be solved by using SSE and saving only the used
> registers, and the second with lazy TS flag restoring.
> 

Again, I want to see a strong use case before even *considering* making
the rules we already have any more complex.

	-hpa
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