linux-kernel - Re: [PATCH] use movntq version of fast_clear_page/fast_copy

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Date:	Wed, 14 Feb 2007 22:23:28 +0100
From:	Arjan van de Ven <arjan@...radead.org>
To:	Marcelo Tosatti <marcelo@...ck.org>
Cc:	Dave Jones <davej@...hat.com>,
	Jordan Crouse <jordan.crouse@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] use movntq version of fast_clear_page/fast_copy_page
	on Geode

On Wed, 2007-02-14 at 18:17 -0200, Marcelo Tosatti wrote:
> On Wed, Feb 14, 2007 at 02:55:46PM -0500, Dave Jones wrote:
> > On Wed, Feb 14, 2007 at 05:08:39PM -0200, Marcelo Tosatti wrote:
> >  > 
> >  > movntq instruction is supported by Geode CPU's, so use
> >  > fast_clear_page/fast_copy_page versions that have it.
> > 
> > it's supported, but is it a win ?
> > The same was also true of the VIA C3/C7's, but due to
> > poor memory bandwidth, it turned out to be slower in most cases.
> 
> Do you have the numbers for VIA C3/C7 around?
> 
> The Geode benefits from movntq instead of movq:
> 
> [marcelo@...alhost ~]$ cat /proc/cpuinfo
> processor       : 0
> vendor_id       : Geode by NSC
> cpu family      : 5
> model           : 5
> model name      : Geode(TM) Integrated Processor by National Semi
> stepping        : 2
> cpu MHz         : 364.898
> cache size      : 32 KB
> ...
> 
> [marcelo@...alhost ~]$ wget http://www.fenrus.demon.nl/athlon.c
> ...


btw there is a caveat with this program: you don't see that this evicts
the data RIGHT AFTER THE COPY, so if you use it again you pay AGAIN the
memory bandwidth price...

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