linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <20091108193618.GB4186@elf.ucw.cz>
Date:	Sun, 8 Nov 2009 20:36:19 +0100
From:	Pavel Machek <pavel@....cz>
To:	Sven-Haegar Koch <haegar@...net.de>
Cc:	Matteo Croce <technoboy85@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org
Subject: Re: i686 quirk for AMD Geode

On Sun 2009-11-08 20:29:55, Sven-Haegar Koch wrote:
> On Sun, 8 Nov 2009, Pavel Machek wrote:
> 
> > On Sun 2009-11-08 18:40:06, Matteo Croce wrote:
> > > On Sun, Nov 8, 2009 at 6:37 PM, Pavel Machek <pavel@....cz> wrote:
> > > > On Fri 2009-11-06 23:18:06, Matteo Croce wrote:
> > > >> On Fri, Nov 6, 2009 at 5:44 PM, H. Peter Anvin <hpa@...or.com> wrote:
> > > >> > On 11/06/2009 06:59 AM, Matteo Croce wrote:
> > > >> >> indeed it has MMX, MMXEXT and CMOV, just lacks the long NOP instruction (NOPL).
> > > >> >
> > > >> > MMX and MMXEXT are hardly hallmarks of i686, which leaves only cmov.
> > > >> > I'm somewhat wondering about the general value of this patch; is i686
> > > >> > code really that much faster on Geode that it's worth it?
> > > >> >
> > > >> > ? ? ? ?-hpa
> > > >> >
> > > >> > --
> > > >> > H. Peter Anvin, Intel Open Source Technology Center
> > > >> > I work for Intel. ?I don't speak on their behalf.
> > > >> >
> > > >> >
> > > >>
> > > >> yes, I did some test like gzip, bzip2, lame etc and they give more or less
> > > >> the same results of dhrystone
> > > >>
> > > >> root@...x:/usr/src# CFLAGS='-march=i586' ./dry.c
> > > >> Microseconds for one run through Dhrystone:        1.4
> > > >> Dhrystones per Second:                          740741
> > > > ...
> > > >> root@...x:/usr/src# CFLAGS='-march=i686' ./dry.c
> > > >> Trying 5000000 runs through Dhrystone:
> > > >> Microseconds for one run through Dhrystone:        1.2
> > > >> Dhrystones per Second:                          841751
> > > >
> > > > Teach gcc that geodelx exists? No need to break kernel for that... and
> > > > you probably can gain even bigger gains.
> 
> But no standard distribution will be made available in a geode special 
> version - not enough machines in the marekt. So I think it is better to 
> be able to use the i686 specific things they already support, like 
> libc6-686 from debian for example.

So hack your distribution to use libc6-686 if you know that it is
safe... (that is no NOPL usage there). Still no need to break
/proc/cpuinfo.
									Pavel

-- 
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