Red Hat Bugzilla – Bug 222532
no centrino speedstep with xen
Last modified: 2007-11-30 17:11:53 EST
Description of problem:
no speedstep support with xen
Version-Release number of selected component (if applicable):
CPU: Intel(R) Core(TM)2 CPU T7600 @ 2.33GHz
Machine: Dell Precision Mobile Workstation M90
Steps to Reproduce:
1. Boot into kernel-xen
2. Check /sys/devices/system/cpu/cpu0/cpufreq
3. it is not present
The centrino speedstep should be available due to
a patch by Matt Yourst
There is a release note in cpuspeed-1.2.1-1.43
that it does not start on xen kernels.
If xen kernels should provide speedstep, this should be re-enabled as well.
The reason that frequency scaling is disabled is not because speedstep doesn't
work under Xen. It *does* work, if enabled --- but it completely fails to take
account of activity in domains other than the host dom0. So if you have a guest
domU busy on the machine and dom0 is idle, frequency scaling will slow the host
down to its slowest setting.
In the future we hope for this to be fixed upstream, but we have no plans to
address it in FC-6 at this time.
Sorry, I forgot a diagnostic message. The FC6 xen kernel does not load the
module acpi_cpufreq during boot and is therefore not able to set up speedstep.
FATAL: module acpi_cpufreq not found
Please advise how I can load this module under xen, since you mention "it *does*
The reason is: on dual core laptops, missing speedstep is annoying since energy
consumption and heat is significantly higher.
I think slowing down the whole activity of all xen domains is the expected
behavior and I could live with only accounting of cpu activity in dom0.