Microsoft KB Archive/167050

= CPU Usage Limited to 100% on Multiprocessor Computer =

Article ID: 167050

Article Last Modified on 11/1/2006

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APPLIES TO


 * Microsoft Windows NT Workstation 3.51
 * Microsoft Windows NT Server 3.51

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This article was previously published under Q167050



SYMPTOMS
CPU usage at the process level appears to be truncated at 100 percent on multiprocessor systems. When summing the thread data on multiprocessor computers for a busy process, the sum will exceed 100 percent while the process metric will only show 100 percent. As the collection interval increases, the sum of the thread CPU usage does not equal the process metrics, even when the usage is less than 100 percent of a single CPU.



CAUSE
All percentages are capped at 100 percent.



RESOLUTION
After applying the hotfix mentioned below, the following registry parameter will allow the percentage to exceed 100 percent.

WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk.

Registry value:

Location: HKEY_CURRENT_USER\Software\Microsoft\PerfMon

Parameter: CapPercentsAt100

Value: 1 default percent capped at 100.

Value: 0 New functionality, percent greater than 100.



STATUS
Microsoft has confirmed this to be a problem in Windows NT version 3.51 and 4.00. This problem was corrected in the latest Microsoft Windows NT 4.0 U.S. Service Pack. For information on obtaining the service pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

Additional query words: smp performance monitor

Keywords: kbbug kbfix kbusage KB167050

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