Negative Values in Performance Monitor Data

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0

IMPORTANT: This article contains information about editing the registry. Before you edit the registry, make sure you understand how to restore it if a problem occurs. For information about how to do this, view the "Restoring the Registry" Help topic in Regedit.exe or the "Restoring a Registry Key" Help topic in Regedt32.exe.

SYMPTOMS

Performance Monitor data exported to a file may include negative values. These values will correspond to extreme spikes when viewed in Chart view and cannot be scaled down. The Pages/sec counter of the Memory object is one example. Other counters will be affected as well.

CAUSE

A condition exists where negative values are not reset to 0. Negative values can occur when a counter rolls over. The maximum value for any counter is 0xFFFFFFFF.

MORE INFORMATION

Values are determined by taking the old value and subtracting it from the new one. The resulting difference is the data point. The following example uses the Pages/sec counter.

If the last value was 0x100 and the new value is 0x200, the pages per second is 0x100. If the last value is 0xFFFFFF80 and the ULONG rolls over to 0xC0 (that is 0x140 pages between samples), a negative value occurs (0xC0 - 0xFFFFFF80 = negative number).

Resetting unreadable or uninterpretable data (such as negative values) can mask problems in the counters themselves. The registry parameter below determines whether Performance Monitor logs error and warning events in the Event Viewer event log when it fails to retrieve data or when it retrieves unreadable or uninterpretable data (such as negative time). By default, this value entry does not appear in the registry and Performance Monitor does not log data errors or notify the user that it has received bad data; it just displays 0 or 100%, depending on the counter. Perform the following steps to enable logging:

WARNING: Using Registry Editor incorrectly can cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that problems resulting from the incorrect use of Registry Editor can be solved. Use Registry Editor at your own risk.

For information about how to edit the registry, view the "Changing Keys And Values" Help topic in Registry Editor (Regedit.exe) or the "Add and Delete Information in the Registry" and "Edit Registry Data" Help topics in Regedt32.exe. Note that you should back up the registry before you edit it.

1. Run Registry Editor (Regedt32.exe).

2. Go to the following key:

         HKEY_CURRENT_USER\Software\Microsoft\PerfMon
   

3. Click Add Value on the Edit menu.

4. Add the following value:

         Value Name: ReportEventsToEventLog
         Data Type: REG_DWORD
         Range: 0 or 1
         Default: 0
   

   Set the data value to 1.

5. Click OK and then quit Registry Editor.

6. Shut down and restart Windows NT.

STATUS

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.