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?

ymajoros

Posted 2011-05-30T06:50:29.403

Reputation: 417

1Do do know that Process Explorer in order to run will have to take CPU time eventually? There's nothing wrong with it taking ~20%. What exactly do you think is wrong with your values? – slhck – 2011-05-30T07:03:56.070

Don't forget that Process Explorer will automatically up itself to "High" priority (Task Manager does the same). – user1686 – 2011-05-30T13:12:16.050

@slhck: 20% is a lot. Got about 0.80% on a slightly better machine (~2 % when sorting by cpu time; why, btw?). – ymajoros – 2011-05-31T14:04:21.060

Answers

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...

Leftium

Posted 2011-05-30T06:50:29.403

Reputation: 8 163

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

resmon

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

Moab

Posted 2011-05-30T06:50:29.403

Reputation: 54 203

6-10% when left running – ymajoros – 2011-05-31T14:15:53.613

What processes are using this 6-10%? Did you try running process monitor as Administrator? Which version of Process Monitor? – Moab – 2011-05-31T21:34:05.883

Latest version of Process Monitor. 6-10% is from resmon. About half of it comes from perfmon.exe itself, 1.4% from "System interrupts". – ymajoros – 2011-06-01T14:00:01.433

6-10 for resmon seems high, mine only shows 1%, occasionally 2%. Sorry I meant to say Process Explorer, try re-downloading it and running as Administrator. – Moab – 2011-06-01T15:41:23.887

I always run it as administrator. – ymajoros – 2011-06-02T05:38:00.033

The only work-around for this has been to use ProcExp v14.01. Unfortunately it doesn't work on Win8 well, so the best work-around for now is Process Hacker - which is now capable enough to have a chance of replacing ProcExp.

Here's a screnshot of the problem:

enter image description here

RomanSt

Posted 2011-05-30T06:50:29.403

Reputation: 7 830

What problems do you have with ProcExp? I'm running v14.0.0.0 on Win8 without any problems. – Leftium – 2013-03-05T01:28:56.310

@Leftium I don't remember exactly; I think it locked up when I did something simple. But no worries; I've switched to ProcessHacker and I see no reason to ever look back; I couldn't find a single missing feature and a bunch of improvements I've wanted for ages. Highly recommended. – RomanSt – 2013-03-05T09:37:12.473

You could try installing SysInternals (owned by Microsoft for quite sometime now) Process Monitor and see if you get different values.

icc97

Posted 2011-05-30T06:50:29.403

Reputation: 396