AW: How to use Px/Cx for power saving?

[Carsten Schiers <carsten@schiers.de>]

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@jp.fujitsu.com>
Gesendet: Mit, 14.1.2009 15:32
An: xen-devel <xen-devel@lists.xensource.com> ; "Tian, Kevin" <kevin.tian@intel.com> ; Yu Ke <ke.yu@intel.com>
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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