HP ProLiant Server Power Management for Red Hat Enterprise Linux 6.x

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Example 1: Output for CPU 0 in OS Control mode

# cpufreq-info -c 0

cpufrequtils 007: cpufreq-info (C) Dominik Brodowski 2004-2009

Report errors and bugs to cpufreq@vger.kernel.org, please.

analyzing CPU 0:

driver: acpi-cpufreq

CPUs which run at the same hardware frequency: 0

CPUs which need to have their frequency coordinated by software: 0

maximum transition latency: 10.0 us.

hardware limits: 1.20 GHz - 2.00 GHz

available frequency steps: 2.00 GHz, 2.00 GHz, 1.90 GHz, 1.80 GHz,

1.70 GHz, 1.60 GHz, 1.50 GHz, 1.40 GHz, 1.30 GHz, 1.20 GHz

available cpufreq governors: ondemand, userspace, performance

current policy: frequency should be within 1.20 GHz and 2.00 GHz.

The governor "ondemand" may decide which speed to use

within this range.

current CPU frequency is 1.20 GHz.

You can dynamically change the governor used under the OS Control mode by modifying the value in the

/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor file for each CPU. RHEL 6.x provides the

cpufreq-set command to select the governor. For more information about the cpufreq-util and cpufreq-

set commands, refer to the RHEL 6.x man pages.

Collaborative power control with RHEL 6.x

When ProLiant servers are under OS Control mode for power management, power capping may still be imposed by the

platform without the knowledge of the operating system. First introduced on Intel-based G6 ProLiant servers and

included in all Gen8 ProLiant servers, OS Control mode enables the server and the OS to collaborate on power

management. HP provides the Collaborative Power Control (CPC) mechanism, which is capable of providing capping-

related feedback to the operating system and can collaborate with the operating system to manage the power

consumption of a server. This combination provides the quick response time of HP Dynamic Power Savings and still

provides correct processor power information to the operating system.

CPC uses the Processor Clocking Control (PCC) interface, which is an interface for coordinating processor performance

between the platform firmware and the operating system. The PCC interface, jointly developed by HP and Microsoft, is

publicly available, allowing other platform vendors the option of implementing it. For more information on PCC, see:

http://www.acpica.org/download/Processor-Clocking-Control-v1p0.pdf

Platform firmware releases for Intel-based ProLiant G6 servers from August 2009 and later include support for CPC.

When a CPC-enabled server is configured in HP Dynamic mode, the firmware does not present P-state information to the

operating system. Instead, the firmware presents the minimum and maximum frequencies the processor supports,

allowing the OS to choose any frequency within that range, rather than restricting the processor to specific P-states. If

the processor is capped at that time for any reason, then the platform firmware will inform the OS that the request could

not be accomplished due to capping. When capping is not configured, the PCC driver still continues to function in lieu of

the P-state driver. Example 2 shows a sample output for CPU 0 for a Gen8 server running under RHEL 6.1. In this

example, notice that the driver is pcc-cpufreq. Only the minimum and maximum frequency limits are displayed.

Unlike under OS Control, there are no preset frequency steps.

Example 2: Output for CPU 0 in HP Dynamic mode with CPC enabled