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Date:	Sat, 28 Feb 2009 17:38:13 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>,
	torvalds@...ux-foundation.org, mingo@...e.hu,
	nickpiggin@...oo.com.au, sqazi@...gle.com,
	linux-kernel@...r.kernel.org, tglx@...utronix.de
Subject: Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache()

On Sun, 1 Mar 2009 02:48:22 +0100
Andi Kleen <andi@...stfloor.org> wrote:

> > the entire point of using movntq and friends was to save half the
> 
> I thought the point was to not pollute caches? At least that is 
> what I remember being told when I merged the patch.
> 

the reason that movntq and co are faster is because you avoid the
write-allocate behavior of the caches....

the cache polluting part of it I find hard to buy for general use (as
this discussion shows)... that will be extremely hard to measure as
a real huge thing, while the WA part is like a 1.5x to 2x thing.


-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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