Hi,
cpufreq support can be either handled by xen or dom0-kernel. You have to 
specify cpufreq=xen or
cpufreq=dom0-kernel as parameters when starting the hypervisor.
Kevin Tian wrote yesterday:
 > It's intentional since Xen itself supports cpufreq now. To avoid 
 > dependency on dom0's CONFIG_CPU_FREQ and also intrusive 
 > checks on whether external control is enabled in every linux
 > cpufreq drivers, CPU_FREQ in dom0 is silented by default now.
 > It's not a neat approach, but makes sense since xen controlled
 > cpufreq is sure a better model. You can enable CPU_FREQ in
 > dom0 manually though, by removing below dependency.
 > (drivers/cpufreq/Kconfig)
 > config CPU_FREQ
 > bool "CPU Frequency scaling"
 > ----> depends on !PROCESSOR_EXTERNAL_CONTROL
 > However once that dependency is removed, there's no automatic
 > check to avoid confliction when dom0 and xen both want to
 > control freq change, and then you should keep an eye yourself.
For AMD, pre-Family 10 CPUs you are supposed to use dom0-kernel, where you can 
encounter problems
with TSC drifts. For other CPUs, I have no knowledge. Family 10 CPUs will have 
P-State invariant
TSCs and will be should be supported by xen cpufreq. C-State handling is 
switched on by cpuidle as
parameter.
Note: xenpm is used to handle xen cpufreq support. In dom0-kernel, you use the 
dom0 tools.
BR,
Carsten.
----- Originalnachricht -----
Von: Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>
Gesendet: Mit, 14.1.2009 15:32
An: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx> ; "Tian, Kevin" 
<kevin.tian@xxxxxxxxx> ; Yu Ke <ke.yu@xxxxxxxxx>
Betreff: [Xen-devel] How to use Px/Cx for power saving?
Hi,
If we want to use ACPI power saving(Cx/Px), how do we use them?
I tried to turn CONFIG_xxxx of cpufreq on with linux-2.6.18-xen.hg,
but I couldn't turn them on.
Also xenpm said the following error.
# xenpm get-cpuidle-states
Xen cpuidle is not enabled!
# xenpm get-cpufreq-states
Xen cpufreq is not enabled!
What should I do?
If there are some good documents, please tell me.
Best Regards,
Akio Takebe
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