Xen devel - Jan 2009 - AW: AW: How to use Px/Cx for power saving?

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@intel.com>
Gesendet: Don, 15.1.2009 03:40
An: ''Akio Takebe'' <takebe_akio@jp.fujitsu.com>
Cc: Carsten Schiers <carsten@schiers.de> ; xen-devel
<xen-devel@lists.xensource.com> ; "Yu, Ke"
<ke.yu@intel.com>
Betreff: RE: AW: [Xen-devel] How to use Px/Cx for power saving?
>From: Akio Takebe [mailto:takebe_akio@jp.fujitsu.com] 
>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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>From: Carsten Schiers [mailto:carsten@schiers.de] 
>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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> Also, is acpi_cpufreq an alternative to e.g. powernow-k8 or 
> speedstep-centrino? 
It is for Intel parts, but AMD power management does not
quite follow the ACPI specification and acpi-cpufreq does
not support it.

For AMD parts, use powernow-k8.

-Mark Langsdorf
Operating System Research Center
AMD


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