CPU Usage Limited to 100% on Multiprocessor Computer

• Microsoft Windows NT Workstation versions 3.51, 4.00
• Microsoft Windows NT Server versions 3.51, 4.00

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 : kbusage kbfix4.00.sp2 NTSrvWkst ntutil
Version : winnt:3.51,4.00
Platform : winnt
Issue type : kbbug