optimized Geode code (was Re: OLPC upgrades)

S Page info at skierpage.com
Sat Feb 7 19:40:56 EST 2009


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.)

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 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 for all you do,
--
=S Page


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