[Xen-devel] Question about support for acpi_cpufreq module in Xen

["Santos, Jose Renato G" <joserenato.santos@xxxxxx>]

Does Xen support changes to the processor P-state using acpi_cpufreq module?

I have an Intel core2-duo machine with 2 physical CPUs (4 logical CPUs in 
total) and acpi_cpufreq does not seem to work properly

When I run the command cpufreq-info (in dom0), I get the following:

> cpufrequtils 002: cpufreq-info (C) Dominik Brodowski 2004-2006
> Report errors and bugs to linux@xxxxxxxx, please.
> analyzing CPU 0:
>   driver: acpi-cpufreq
>   CPUs which need to switch frequency at the same time: 0
>   hardware limits: 2.00 GHz - 3.00 GHz
>   available frequency steps: 3.00 GHz, 2.00 GHz
>   available cpufreq governors: userspace, performance
>   current policy: frequency should be within 2.00 GHz and 3.00 GHz.
>                   The governor "userspace" may decide which speed to use
>                   within this range.
>   current CPU frequency is 3.00 GHz.
> analyzing CPU 1:
>   driver: acpi-cpufreq
>   CPUs which need to switch frequency at the same time: 1
>   hardware limits: 2.00 GHz - 3.00 GHz
>   available frequency steps: 3.00 GHz, 2.00 GHz
>   available cpufreq governors: userspace, performance
>   current policy: frequency should be within 2.00 GHz and 3.00 GHz.
>                   The governor "userspace" may decide which speed to use
>                   within this range.
>   current CPU frequency is 3.00 GHz.
> analyzing CPU 2:
>   no or unknown cpufreq driver is active on this CPU
> analyzing CPU 3:
>   no or unknown cpufreq driver is active on this CPU

It seems acpi_cpufreq is not recognizing 2 of my CPUs.

I think this problem is somehow related to the fact that if two cores share the 
same socket they cannot be set to distinct Power states.
Xen is reporting that the 4 CPUs are in 4 distinct physical CPUs (siblings=1) 
when each physical CPU has 2 cores, and this may be confusing acpi_cpufreq. 
(see the difference in /proc/cpuinfo between Xen and Linux in the attached 
files).

Is this a well known problem? Is there any way to fix this? I thought Xen has 
been fixed to report the right physical CPU topology but maybe I am wrong.

Any help would be greatly appreciated

Thanks

Renato

PS - I am using xen-unstable c/s 17193:f33328217eee

cpuinfo_linux
Description: cpuinfo_linux

cpuinfo_xen
Description: cpuinfo_xen

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