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

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Date:	Wed, 14 Feb 2007 18:17:36 -0200
From:	Marcelo Tosatti <marcelo@...ck.org>
To:	Dave Jones <davej@...hat.com>, Marcelo Tosatti <marcelo@...ck.org>,
	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, 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
...

[marcelo@...alhost ~]$ ./athlon
Athlon test program $Id: fast.c,v 1.6 2000/09/23 09:05:45 arjan Exp $
clear_page() tests
clear_page function 'warm up run'        took 9565 cycles per page
clear_page function '2.4 non MMX'        took 3347 cycles per page
clear_page function '2.4 MMX fallback'   took 3389 cycles per page
clear_page function '2.4 MMX version'    took 2920 cycles per page
clear_page function 'faster_clear_page'  took 2912 cycles per page
clear_page function 'even_faster_clear'  took 2863 cycles per page

copy_page() tests
copy_page function 'warm up run'         took 9409 cycles per page
copy_page function '2.4 non MMX'         took 13161 cycles per page
copy_page function '2.4 MMX fallback'    took 13033 cycles per page
copy_page function '2.4 MMX version'     took 9288 cycles per page
copy_page function 'faster_copy'         took 9806 cycles per page
copy_page function 'even_faster'         took 8990 cycles per page

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