OK, I have found the change and ported it into the 2.6.18-xen-3.1-2
waldi kernel. Fortunately, the Debian Xen 3.2.1 Hypervisor from Lenny,
which is used by my dsitribution (c't-Server), already implements the
xenpf_cpuidletime hypercall #53, which is needed. Some changes here 
and there where necessary, too.
Now, when setting the ondemand govenor, the system behaves as expected.
Still (as with userspace govenors), there are 
 - powernow-k8: error - out of sync, fix 0xd 0x2, vid 0xe 0x16
 - Timer ISR/0: Time went backwards: delta=
messages, when the p-states are changed. 4050e, as already mentioned,
dual-core, single socket.
Can I safely ignore them or do I have to take care somewhere...?
BR,
Carsten.
Von: Niraj Tolia 
Gesendet: Mit, 7.1.2009 22:53
An: Carsten Schiers 
Cc: jbeulich ; mark.langsdorf ; xen-devel 
Betreff: Re: RE: [Xen-devel] AMD P-States not recognized for Xen 3.3 and 3.4
On Wed, Jan 7, 2009 at 1:02 PM, Carsten Schiers wrote:
So having read that, I have to summarize that working with the
Xen 3.2.1 / 2.6.18-xen-3.1-2 kernel / cpufreq=dom0-kernel team
seems to be the best option.
Only drawback is for sure that typical tools, like powernowd is
only using Dom0 load. But I think I could possibly try to modify
powernowd or another tool to use what e.g. xentop is producing
as output, so that I tune up the system a bit when there is a
noticable bigger load than the 10% it is typically sleeping at.
If you are using the in-kernel ondemand governor (cpufreq=dom0-kernel), it will 
look at complete system load and not just dom0. Look at cpufreq_ondemand.c in 
the 2.6.18-xen.hg tree for more info.
Cheers,
Niraj
 
Or am I wrong?
Thanks,
Carsten.
-----Ursprüngliche Nachricht-----
Von: Langsdorf, Mark [mailto:mark.langsdorf@xxxxxxx]
Gesendet: Mittwoch, 7. Januar 2009 21:22
An: Carsten Schiers; xen-devel@xxxxxxxxxxxxxxxxxxx
Betreff: RE: [Xen-devel] AMD P-States not recognized for Xen 3.3 and 3.4
> > ... but was told that it is intentional that there's no
> code to handle these.
>
> Hm. And for what reason it does work in dom0-kernel? Because
> it's done by powernow-k8.ko and userspace software?
Correct. The family 0xf P-state interface is significantly
more complicated than the Family 0x10/architectural P-state
interface. Porting it into the Xen hypervisor would possibly
introduce some more stability issues. The architectural
P-state interface is much stabler and smaller, and it made
sense to move it into Xen.
Since the family 0xf P-state interface already existed in the
Linux kernel, it was easy enough to allow Linux dom0s to use
it for RevF systems. Sadly, it's still got some problems
due to the use of TSC as a time source.
-Mark Langsdorf
Operating System Research Center
AMD
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Niraj Tolia, Researcher, HP Labs
http://www.hpl.hp.com/personal/Niraj_Tolia/
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