On HP G5 hardware and above, "no or unknown cpufreq driver is active on this CPU"

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Environment

SUSE Linux Enterprise Server 11
SUSE Linux Enterprise Server 11 Service Pack 1
SUSE Linux Enterprise Server 10
SUSE Linux Enterprise Server 10 Service Pack 1
SUSE Linux Enterprise Server 10 Service Pack 2
SUSE Linux Enterprise Server 10 Service Pack 3

Situation

On HP hardware it may appear that the utilities in cpufrequtils are not working as no driver is loaded. The command cpufreq-info gives output similar to:

cpufrequtils 004: cpufreq-info (C) Dominik Brodowski 2004-2006
Report errors and bugs to http://bugs.opensuse.org, please.
analyzing CPU 0:
no or unknown cpufreq driver is active on this CPU
analyzing CPU 1:
no or unknown cpufreq driver is active on this CPU

and cpufreq-info -d gives no output.

Resolution

In such a case, the reason may be that the Power Regulator value in RBSU (ROM Based Setup Utility) is set to HP Dynamic. The following HP document may be useful:
http://h20000.www2.hp.com/bc/docs/support/SupportManual/c02011017/c02011017.pdf

On page 3:

"HP Dynamic Control of P-states resides with the firmware. This mode allows the firmware to change the Pstate of the processor to match the server load. It is the default mode on HP ProLiant G5 and later servers."

Changing the Power Regulator BIOS setting to "OS Control", will allow a driver to be loaded. For instance the powernow-k8 will load as the P-state driver on AMD-based ProLiant servers (such as the BL685c G7).

Disclaimer

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