Event 37: The speed of processor # in group # is being limited by system firmware

On some of our HP DL360G6 servers, the following warning (event id 37) showed up in the event log of Windows 2008 R2

Log Name:      System
Source:        Microsoft-Windows-Kernel-Processor-Power
Date:          12/21/2009 5:04:12 PM
Event ID:      37
Task Category: (7)
Level:         Warning
Keywords:     
User:          SYSTEM
Computer:      <servername>
Description:
The speed of processor 0 in group 0 is being limited by system firmware. The processor has been in this reduced performance state for 2139 seconds since the last report.”

To solve this error, do the following:

1. In Windows, check your Power Options. Make sure that your Power Scheme is set to High Performance, and check that every option is set to “Always On”.
2. Make sure you have installed all latest drivers and firmware, especially for your motherboard and CPU.
3. Reboot your computer and go to your BIOS settings. Make sure that your power settings are set to maximum. This differs from coputer to computer.

In case the error occurs on a HP server, you should set in the Minimum Processor Idle Power State “No C-states”:

1. Enter BIOS by pressing F9 on POST
2. Navigate to “Power Management Options” => “Advanced Power Management Options” => “Minimum Processor Idle Power State”
3. Choose “No C-States

Hope this helps one of you. If something is not clear, please leave a comment.