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Date:	Sun, 1 Mar 2009 03:07:08 +0100
From:	Andi Kleen <>
To:	Arjan van de Ven <>
Cc:	Andi Kleen <>, "H. Peter Anvin" <>,
	David Miller <>,,,,,,
Subject: Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache()

On Sat, Feb 28, 2009 at 05:38:13PM -0800, Arjan van de Ven wrote:
> On Sun, 1 Mar 2009 02:48:22 +0100
> Andi Kleen <> 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....

Not faster than rep ; movs which does similar magic anyways. Of course it being
magic it can vary a lot and is somewhat unpredictable.

Also in my experince movnt is not actually that much faster for small 
transfers (as in what the kernel mostly does) 


-- -- Speaking for myself only.
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