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

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

>From: Carsten Schiers [mailto:carsten@xxxxxxxxxx] 
>Sent: Thursday, January 15, 2009 6:54 PM
>
>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?

It's implicitly enforced within Xen once you have dom0-kernel to
control cpufreq.

>
>Also, is acpi_cpufreq an alternative to e.g. powernow-k8 or 
>speedstep-centrino? 

acpi_cpufreq is a more generic driver as long as corresponding
ACPI tables are reported, which is the default one now in native
Linux kernel. If underlying BIOS doesn't conform to ACPI spec,
then you need try specific cpufreq driver like speedstep-centrino
then.

although xen controls cpufreq itself now, xen still depends on
dom0's ACPI parser to retrieve necessary Px information. That's
why I said that xen controlled cpufreq should work if you could
use acpi_cpufreq driver on native Linux which indicates a ACPI
compliant system.

>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).

I don't know AMD platform. But on most Intel platforms 
acpi_cpufreq should work well on native and so does Xen side.

Thanks,
Kevin
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