Re: AW: [Xen-devel] How to use Px/Cx for power saving?

[Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>]

Hi, Carsten

Thank you for your infomation.
I didn't check the mail, sorry.
It's helpful. Is FREQCTL_none the default value?
If we use FREQCTL_dom0_kernel, xen/guests don't use cpufreq?

Best Regards,

Akio Takebe

Carsten Schiers wrote:
> 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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