optimized Geode code (was Re: OLPC upgrades)

Bobby Powers bobbypowers at gmail.com
Sat Feb 7 21:33:14 EST 2009


2009/2/7 Tiago Marques <tiagomnm at gmail.com>:
> On Sun, Feb 8, 2009 at 12:40 AM, S Page <info at skierpage.com> wrote:
>>
>> Tiago Marques wrote:
>>>
>>> That software is still not compiled for the Geode LX, which further
>>
>> slows it down.
>>>
>>> As you say, everything uses CPU on the Geode. Things like
>>
>> decompressing can be made, probably, a lot faster just by using compiler
>> optimizations. Has this been considered in any way for future releases?
>>>
>>> From my professional experience, compiler optimizations can account
>>
>> for 10-30% (or more) free performance.
>>
>> It seems the binaries in the OLPC OS image are just generic 386 arch
>> binaries.  (Is there a way to definitively tell?  A build log like
>> <http://xs-dev.laptop.org/~cscott/xo-1/streams/joyride/latest/devel_jffs2/build.log>
>> is unclear.)
>
> file doesn't say much, everything I have compiled with -march=i686 still
> shows up as i386 binary. I don't know of anything that might tell us that.

well we use standard Fedora repositories, so I think everything is
i386.  It would be interesting to see if it actually made a
difference, if there were real performance increases perhaps Geode can
be added as a supported arch in Koji.

bobby

>>
>> This is the case even in the jffs2 OS images that will never be used on
>> anything but the stable XO hardware (or in emulation, which AIUI already
>> requires AMD CPU emulation because of the tuned kernel).
>>
>> So every OLPC and activity binary should be compiled with -mtune=geode
>> (optimized for Geode, but still runs on any i386), and in jffs2 images they
>> should be compiled with -march=geode (only runs on Geode). ("Should" as in
>> "I'd like a pink pony too" ;-) .)
>
> I've read some reports that indicate that using -mtune should be good enough
> for added performance, although I mostly compile with -march for my systems.
> I never bothered to check but I'll run some tests on the XO to see if it's
> significant and worth the extra effort(if feasible, as you say).
>
>>
>> I assume this is what GentooXO does,
>> http://www.gentooxo.org/features.shtml
>>
>> https://dev.laptop.org/ticket/118 is the tracking ticket,
>> http://wiki.laptop.org/go/Geode_optimization_effort the page.
>
> Thanks!
> Best regards,
>                         Tiago Marques
>
>>
>> Thanks for all you do,
>> --
>> =S Page
>
>
>
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