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SubjectRe: Cyrix patch : Proposal?

Teunis, I would *not* want to see the (fixed) 2.1.39 Cyrix patch go into
the kernel source, as it stands now.

I have a simple technical reason, and a more "philosophical" reason for

Technical: no performance gains

The main performance improvement that can be had by adapting Linux
operation to a 6x86 processor is the correct setup of the ARR registers.
This can bring a 30-50% CPU/video memory bandwidth improvement.

The 2.1.39 patch does *not* set the ARRs, because this would imply the
detection of the linear frame buffer address, which changes from system
to system.

The other performance features bring a *measured* performance
improvement of less than 0.5%. This is insignificant IMHO.

Philosophical: kernel pollution vs. user-space utility

Everything (nearly) the patch does can be done in user-space using the
set6x86 GPLed utility written by Koen Gadeyne. You don't have to
recompile your kernel everytime a 6x86 feature needs to be tested or
changed. And set6x86 allows setting the ARRs.

The only thing set6x86 cannot do is implement the 6x86 VSPM feature,
which only works in some 6x86 revisions, has been dropped in the new
6x86MX and does not provide any measurable performance improvement.

So I would prefer to keep the kernel source as clean as possible,
without adding every possible trick or gadget (this also applies to
other tricks and gadgets that unfortunately have gone into the kernel
source, sometimes causing strange side-effects).

In some cases a patch is needed, but the 2.1.39 Cyrix patch is not.

OTOH it's an excellent patch and I thank Mike Jagdis (the original
author) for it. It's a clean patch and the accompanying documentation is
of the highest quality (quite exceptional when it comes to kernel

I will give you another example of something that should be set using a
user-space utility: IDE driver parameters. We have hdparm thankfully,
but imagine what would have happened if M. Lord had decided to make all
the hdparm options kernel compilation option? I guess he made a good
decision, and I propose we follow his example when it comes to the cyrix
2.1.39 patch.


Andrew D. Balsa
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