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RE: [Xen-users] Setting CPU (core) frequency from dom0

To: "'bmunoz@xxxxxxx'" <bmunoz@xxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-users] Setting CPU (core) frequency from dom0
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Thu, 20 Nov 2008 11:05:13 +0800
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Thread-topic: [Xen-users] Setting CPU (core) frequency from dom0
Your description is basically correct. Do you want to control cpu frequency from dom0 user level, or just try cpufreq governor in dom0? For the former, we're currently adding more flexibility to xen cpufreq (such as user space governor) and control options to xenpm (such as manually changing freq), which is expected to reach xen upstream soon. For the latter, it's suboptimal with limitations which is why xen cpufreq is develeoped. You may manually disable PROCESSOR_EXTERNAL_CONTROL in drivers/acpi/Kconfig to rebuild dom0 kernel for mode A.
 
Thanks,
Kevin


From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Alberto Munoz
Sent: Thursday, November 20, 2008 2:50 AM
To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Setting CPU (core) frequency from dom0

Hello everyone,

I am running some experiments that require changing the frequency of a CPU in a SunFire machine (32-core quad socket AMD Barcelona).

For what I have found (bits and pieces but not a comprehensive description), there are two meachisms for controlling core (most probably socket) frequency in Xen:

A- The older (xen-3.2.1) mechnism through dom0 (option cpufreq=dom0-kernel), which for what I gather uses a module in dom0 (cpufreqd?) that allows one to set cpu frequency.

B- The newer (xen-3.3), which has moved the governor to the hypervisor (option cpufreq=xen), which other than a utility to read processor P and C states (xenpm) does not (yet) allow user (dom0) control of CPU frequency.

My first question is whetherot what I have written above is accurate. My second question is where can I find detailed information on how to set up my system to make use of A above and be able to set cpu frequency "manually" from Dom0 (assuming that is still possible in Xen 3.3).

I am running the latest testing version of Xen 3.3 (about a week old).

Any information would be greatly appreciated.

Thank you,

Alberto
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