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Date: Sun, 1 Mar 2009 03:07:08 +0100
From: Andi Kleen <andi@firstfloor.org>
To: Arjan van de Ven <arjan@infradead.org>
Cc: Andi Kleen <andi@firstfloor.org>, "H. Peter Anvin" <hpa@zytor.com>,
       David Miller <davem@davemloft.net>, torvalds@linux-foundation.org,
       mingo@elte.hu, nickpiggin@yahoo.com.au, sqazi@google.com,
       linux-kernel@vger.kernel.org, tglx@linutronix.de
Subject: Re: [patch] x86, mm: pass in 'total' to __copy_from_user_*nocache()
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References: <alpine.LFD.2.00.0902280904271.3111@localhost.localdomain> <20090228092450.3ded2db5@infradead.org> <alpine.LFD.2.00.0902280935010.3111@localhost.localdomain> <20090228.160651.228301019.davem@davemloft.net> <20090301004003.GF26292@one.firstfloor.org> <49A9D6CA.30906@zytor.com> <20090228163811.48b1de72@infradead.org> <20090301014822.GG26292@one.firstfloor.org> <20090228173813.6d86c0ef@infradead.org>
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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 <andi@firstfloor.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....

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) 

-Andi

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