linux-kernel - Re: x86 memcpy performance

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Message-ID: <20110816074309.GA31781@liondog.tnic>
Date:	Tue, 16 Aug 2011 09:43:10 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	melwyn lobo <linux.melwyn@...il.com>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	borislav.petkov@....com
Subject: Re: x86 memcpy performance

On Tue, Aug 16, 2011 at 12:49:28PM +0530, melwyn lobo wrote:
> We would rather use the 32 bit patch. Have you already got a 32 bit
> patch.

Nope, only 64-bit for now, sorry.

> How can I use sse3 for 32 bit.

Well, OTTOMH, you have only 8 xmm regs in 32-bit instead of 16, which
should halve the performance of the 64-bit version in a perfect world.
However, we don't know how the performance of a 32-bit SSE memcpy
version behaves vs the gcc builtin one - that would require benchmarking
too.

But other than that, I don't see a problem with having a 32-bit version.

> I don't think you have submitted 64 bit patch in the mainline.
> Is there still work ongoing on this.

Yeah, we are currently benchmarking it to see whether it actually makes
sense to even have SSE memcpy in the kernel.

-- 
Regards/Gruss,
    Boris.
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