CHOST: i586 vs. i486 on AMD Geode LX
On my blog post about Installing Gentoo on ALIX.3D3 Mart Raudsepp made an interesting comment: He pointed out, that on AMD Geode CPUs it might be better to use i486 CHOST instead of my used i586, because the CPU is more like a i486 as far as instruction scheduling and times go.
This sounded interesting, so I googled for some benchmark test to measure differences. I found nbench, which measures performance by executing some typical algorithms and compares them to a Pentium 90 based system. So I installed it and run on the i586 CHOST system, then rebuild it completely to i486 CHOST and run it again. The differences are not that huge, but on some algorithms they’re measurable:
The first 13 bars are the different algorithms. The main difference is on the string sort, which is heavily memory dependent. That last 3 rows are a index based on the algorithms. Here is main difference on memory index, as the normalized version shows very clear (positive values mean that i486 is faster):
As there is no significant disadvantage of the i486 CHOST, this seems to be the choice. 
If anybody has other (free) benchmarks to suggest, please let me know.
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May25
9 Responses to “CHOST: i586 vs. i486 on AMD Geode LX”
Hi Twam,
Have to tell you, brilliant blog! I’m planning to buy Alix any time soon, good to know that someone have similar interest and ideas. Hear you soon!
OK, I got a some question:
I can’t find any specification about wireless LAN using USB WLAN adaptor. Have you seen any refer of the supporting list of the USB WLAN adaptor for ALIX.3D3?
Second question, before buy, have you checked CF card for ‘True IDE Mode’? Maybe all cards have these 3 modes right now or I just didn’t notice that?
Support of USB WLANs depends on your Linux Kernel, not the ALIX.3D3. If you use a recent kernel, lots of USB adapters are support. I personally would buy one with a Ralink rt3070 Chipset.
I never saw any CF card, not supporting IDE Mode, but there are different speed they support. If you want a fast one, you should look out für UDMA support, like SanDisk Extreme IV has.
Found a reference to this i486 vs i386 matter from the old geode mailing list, which contains statements of i386 and i486 being a better choice for now from (by now) former AMD Geode team members:
http://209.85.129.132/search?q=cache:itHvjJ468_wJ:geode.insideo.net/info-linux_archives/msg00396.html+geode+i586+i486&cd=10&hl=et&ct=clnk&gl=ee&client=firefox-a
Basically I read out that i586 might become a better choice only after glibc has the geode optimizations we talked about (geode-perf GIT tree on dev.laptop.org/git), until then i486 is better
Thanks for the reference. I shows the same results.
I wanted to test i386 as well, but unfortunately Gentoo doesn’t support i386 anymore (at least for glibc-2.10)
Try using gcc-4.4 with the following options:
-march=geode -falign-functions=0 -falign-jumps=2 -falign-loops=0
-mpreferred-stack-boundary=2 -Wa,-mtune=generic32
Those should be about as close to optimal as you can get for the Geode processors.
Thanks! I’ll try that. But this only optimizes the compiled programs, not the way glibc handles memory.
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