Gentoo's very own Daniel Goller has figured out how to get preemption working on PPC without those horrible segfaults we have all grown to love.
In order to get preemption working simply enable SMP (Symmetric multi-processing support) in your kernel along with the "Preemptible Kernel" option, these can both be found under "Platform options". We are currently investigating why this solves the problems. With preemption enabled you should notice quite a difference in terms of responsiveness whenever running I/O-intense processes. On my desktop for instance I've noticed a huge difference when using my system while compiling complex C++ applications such as KDE or The Battle for Wesnoth. Compilations will generally complete faster with preemption enabled if using more than one make thread (set MAKEOPTS="-j2" in /etc/make.conf to enable two make threads, which should be sufficient on a single-CPU/core system).

We have been testing preemption (with SMP enabled) on a number of ppc systems now (including Pegasos IIs) and have yet to experience a single issue related to it. If you decide to enable it and experience any strange behaviour please report back here.

dholm,

Thanks, I'll give it a try.

--Aaron
Gentoo 2005.0
Kernel: 2.6.12-rc6-love1

Hello!

I have enabled SMP with preemption, and so far my system works ok. Did not help on Openoffice though... Right now kde is on the test... We will see.

preemption will be enabled in the next version of mupper

IMHO vanila kernel even with preempt enable works quite slow. I suggest to try the CK patchest for current 2.6.11 or 2.6.12rc6, both work realy nice with my Pegasos II machine.

http://members.optusnet.com.au/ckolivas/kernel/

If you want to give a try to CK patchset disable preemption. At last on my system preemption + ck works in a realy weird way and suprising slow.

In general ck gives a MUCH better results than preempt enabled kernel ... of coz if you want to patch your kernel with 3rd patches

I've been running pre-emption + SMP for a few days now and haven't had a problem. My system has been very stable even on this experimental kernel that I'm running.
I've been reading good things about -ck patches applied over the 2.6.12-rc6-mm1 kernel. Apparently the latest staircase scheduler is pretty good. I haven't tried it yet, though.

--Aaron
Gentoo 2005.0
Kernel: 2.6.12-rc6-love1

ck-sources will probably be moved into ~ppc soon.

If my endorsement counts for anything, I found the -ck patchset to be very stable on my system.

--Aaron
Gentoo 2005.0
Kernel: 2.6.12-rc6-love1