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

[Carsten Schiers <carsten@xxxxxxxxxx>]

Kevin, did I understand you right, that I have to tare care when using
cpufreq=dom-kernel to pin vcpus to physical cpus? I didn't do anythinh
specific, but xm vcpu-list says:

> Name                                ID  VCPU   CPU State   Time(s) CPU 
> Affinity
> Domain-0                             0     0     0   r--     303.0 0
> Domain-0                             0     1     1   -b-     225.2 1

which looks ok. What would be the implication, if there is a fault? Could
this be the reason for my TSC drifts mentioned elsewhere here on the list?

Also, is acpi_cpufreq an alternative to e.g. powernow-k8 or speedstep-centrino? 
Whereas powernow-k8 works on my system, acpi_cpufreq is reporting a FATAL: 
No such device. It's a quite new board, so I am not sure, whether this means 
the 
BIOS doesn't support it (my asumption is, acpi_cpufreq uses the BIOS instead of 
a CPU-based driver, like powernow-k8).

Thanks for helping me with all that stuff, it's quite complicated if you're new
to it.

BR,
Carsten.

----- Originalnachricht -----
Von: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Gesendet: Don, 15.1.2009 03:40
An: 'Akio Takebe' <takebe_akio@xxxxxxxxxxxxxx>
Cc: Carsten Schiers <carsten@xxxxxxxxxx> ; xen-devel 
<xen-devel@xxxxxxxxxxxxxxxxxxx> ; "Yu, Ke" <ke.yu@xxxxxxxxx>
Betreff: RE: AW: [Xen-devel] How to use Px/Cx for power saving?

>From: Akio Takebe [mailto:takebe_akio@xxxxxxxxxxxxxx] 
>Sent: Thursday, January 15, 2009 10:05 AM
>
>> '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.
>>
>If dom0_max_vcpus < total_phys_cpus, dom0 control only his cpus.
>So other cpus don't enter px/cx state, right?
>And you recommend cpufreq=xen?

Yes, I'm recommending cpufreq=xen which is more efficient and
clearer method. For cpufreq=dom0-kernel, such implication exists
to have dom0 vcpus pinned to corresponding physical cpus with
same number. Unless your platform couldn't work with acpi-cpufreq
driver on native linux, you should always spin on cpufreq=xen. 

Thanks,
Kevin

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