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Date:	Fri, 13 Nov 2009 08:33:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Machek <pavel@....cz>
Cc:	"H. Peter Anvin" <hpa@...or.com>, "Ma, Ling" <ling.ma@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] [X86] performance improvement for memcpy_64.S by
 fast string.


* Pavel Machek <pavel@....cz> wrote:

> > Ling, if you are interested, could you send a user-space test-app to 
> > this thread that everyone could just compile and run on various older 
> > boxes, to gather a performance profile of hand-coded versus string ops 
> > performance?
> > 
> > ( And i think we can make a judgement based on cache-hot performance
> >   alone - if then the strings ops will perform comparatively better in
> >   cache-cold scenarios, so the cache-hot numbers would be a conservative
> >   estimate. )
> 
> Ugh, really? I'd expect cache-cold performance to be not helped at all 
> (memory bandwidth limit) and you'll get slow down from additional 
> i-cache misses...

That's my point - the new code is shorter, which will run comparatively 
faster in a cache-cold environment.

	Ingo
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