linux-kernel - Re: i686 quirk for AMD Geode

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Message-ID: <40101cc30911081147j77f7b81o86f2cc5a869aca1f@mail.gmail.com>
Date:	Sun, 8 Nov 2009 20:47:24 +0100
From:	Matteo Croce <technoboy85@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Sven-Haegar Koch <haegar@...net.de>,
	"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, Nov 8, 2009 at 8:36 PM, Pavel Machek <pavel@....cz> wrote:
> 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
>
> --
> (english) http://www.livejournal.com/~pavelmachek
> (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
>

Better to be sure that a NOPL whouldn't SIGILL your program, isn't it?
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