Why is my CPU usage broken in Process Explorer?

On my system (Windows 7), it seems that Process Explorer is reporting the wrong CPU usage:

• When Firefox is running, I constantly get 30%+
• When I kill Firefox, I still get about the same CPU usage
• If I sort by CPU time, Process Explorer itself is taking between 18% and 22%
• Task Manager reports < 10% (which is still a lot while doing nothing)

… all of this while doing nothing special, just having those apps open.

CPU: Intel Core2 Duo P8600 2.4 GHz

Any ideas or ways to investigate this problem?

Solution 1:

In recent versions of Process Explorer, the CPU usage percentage is calculated differently. According to Mark Russinovich, the author of Process Explorer:

Process Explorer shows actual CPU usage now based on cycle counts. If you have speedstep or other CPU frequency throttling enabled that will cause work consuming some number of cycles to be calculated as a higher percentage of available cycles per second.

If you prefer the old CPU percentage, use a previous version of Process Explorer (v14.01). You could also ask for the old CPU usage percentage in the feature request thread.

Note the "show one graph per CPU" option shows each CPU's usage without accounting for speedstep. However, the other CPU percentage displays are not affected. You can also disable your processor's speedstep, but that seems a little extreme...

Solution 2:

Open the Start Menu and in the search box, type:

resmon

Hit Enter and see what Windows 7 says about the processor usage.