linux-kernel - Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register

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Message-ID: <20121012151410.GB16230@one.firstfloor.org>
Date:	Fri, 12 Oct 2012 17:14:10 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Ma, Ling" <ling.ma@...el.com>
Cc:	Andi Kleen <andi@...stfloor.org>, "mingo@...e.hu" <mingo@...e.hu>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"iant@...gle.com" <iant@...gle.com>
Subject: Re: [PATCH RFC 2/2] [x86] Optimize copy_page by re-arranging instruction sequence and saving register

On Fri, Oct 12, 2012 at 02:54:54PM +0000, Ma, Ling wrote:
> > If you can't test the CPUs who run this code I think it's safer if you
> > add a new variant for Atom, not change the existing well tested code.
> > Otherwise you risk performance regressions on these older CPUs.
> 
> I found one older machine, and tested the code on it, the results between them are almost the same as below(attached cpu info).

Was that a P4 (family 15)? 

Those were the main users. There were a few others, but they are obscure
(early steppings of K8) 

-Andi


-- 
ak@...ux.intel.com -- Speaking for myself only.
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