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

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

Which version are you using? In latest Xen unstable, Xen controlled 
cpufreq is always enabled with userspace governor as the default. 
In such case, you could use xenpm to manually change frequency 
(xenpm set-scaling-speed). Then "xenpm set-scaling-governor"
can be used to choose a new governor like ondemand in the fly.
Before 18950, cpufreq is by default disabled, and you have to add
'cpufreq=xen' in grub to activate xen controlled cpufreq logic. In 
either case, CONFIG_CPU_FREQ in dom0 is not required.

'cpufreq=dom0-kernel' can be always used to allow dom0 control 
freq directly. In such case, Xen itself exits the game, and then you
have to follow below trick to enable CONFIG_CPU_FREQ in dom0
kernel.

For cpuidle, you need a similar boot option 'cpuidle' in xen cmdline
which is off by default. We have plan to allow in-the-fly on/off from
xenpm too.

One of our engineer is working on document side, including all
relevant options and xenpm usage. We tempt to place it on Xen
wiki first, and will let you know for comments. :-)

Thanks,
Kevin

>From: Akio Takebe [mailto:takebe_akio@xxxxxxxxxxxxxx] 
>Sent: Thursday, January 15, 2009 8:02 AM
>
>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
>> 
>> _______________________________________________
>> Xen-devel mailing list
>> Xen-devel@xxxxxxxxxxxxxxxxxxx
>> http://lists.xensource.com/xen-devel
>> 
>
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