[CentOS] Questions on cpu frequency scaling AMD vs. Intel

Kai Schaetzl maillists at conactive.com
Sun Aug 3 18:06:09 UTC 2008

Kai Schaetzl wrote on Sun, 03 Aug 2008 16:31:19 +0200:

> Actually, not the latest kernel. The CentOS xen boot (hypervisor) kernel 
> /xen.gz-2.6.18-92.1.6.el5 (and maybe earlier) ones calculates the frequency 
> correct, the Xen 3.2 boot kernel (xen.gz-3.2) from the Xen 3.2 package 
> offered at xen.org does not. Might there be a kernel parameter or other 
> measure that could correct this?

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 Schätzl, Berlin, Germany
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