Xen users - Aug 2008 - Xen 3.2 on CentOS calculates AMD cpu frequency incorrect

I noticed that booting up with the 3.2 Xen hypervisor on CentOS 5.2 shows 
incorrect cpu frequencies for AMD CPUs. It shows them at 800 MHz, no 
matter which CPU, although running at full speed. The result of this is 
that cpu frequency scaling does not work as the cpufreq module tries to 
adjust to frequencies much higher, although it runs already at full speed.
If I go back to the 2.6 hypervisor kernel coming with CentOS 5.2 the 
frequency is shown correct and frequency scaling works.

Is there kernel parameter or something I could use to correct this 
behavior?

Also, there''s still only the Xen 3.2 rpm packages that were built for 
CentOS 5.1 available for download on xen.org. It would be nice if these 
packages could be updated to Xen 3.2.1 built on CentOS 5.2. (Not only, but 
also in the hope it might fix the problem above.)

Does anyone provide 3.2.1 rpms built on CentOS 5.2 that are not 
specialized to work only in certain environments?

Thanks!

Kai

-- 
Kai Schätzl, Berlin, Germany
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Kai Schaetzl wrote on Sun, 03 Aug 2008 16:33:22 +0200:
> Is there kernel parameter or something I could use to correct this 
> behavior?
After some more research I have found the correct incantation for this. 
The CentOS/RH kernels seem to have this enabled by default, the kernels 
from xen.org have to be "enabled" with a command-line option to the 
hypervisor-kernel (not the CentOS kernel).
kernel /xen.gz-3.2 cpufreq=dom0-kernel

I''m getting now correct readings of the frequencies. And scaling up on 
demand works. At least in dom0. I''m not so sure if it works for domUs
as
well. A quick test showed no ondemand scaling in dom0 when running a cpu-
intensive task in a domU. Anyone has more experience with this?

Kai

-- 
Kai Schätzl, Berlin, Germany
Get your web at Conactive Internet Services: http://www.conactive.com




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