Incorrect C-state data in Windows Server 2008 R2 and in Windows 7

You use the following performance counters to monitor the C-states of a processor on a computer that is running Windows Server 2008 R2 or Windows 7.

• Processor\%C1 Time
• Processor\%C2 Time
• Processor\%C3 Time

However, the collected data does not contain correct information for the current C-state of the processor.

For example, consider the following scenario:

• You have a computer that is running Windows Server 2008 R2 or Windows 7. This computer has an Intel Core i7 Nehalem processor.
• The collected data indicates that the processor is in the C2 state.

In this scenario, the current C-state data is incorrect, and the correct C-state is the C3 state or the C1 state.

This issue occurs because the operating system uses the index of the C-state table instead of the state type variable when it collects the performance counter data for C-states. Therefore, the second entry in the C-state table is assumed to contain the data for the C2 state. However, the second entry in the C-state table is the C3 state on some processors such as Intel Core i7 Nehalem processors. Therefore, the C-state data is collected incorrectly.

This issue will be resolved in Windows Server 2008 R2 Service Pack 1 (SP1) and in Windows 7 Service Pack 1 (SP1).

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about software update terminology, click the following article number to view the article in the Microsoft Knowledge Base: