How is CPU usage computed?

[aperry01]

Hi all,

 

Wonderful app.  Can't believe I only discovered this a couple of weeks ago.  I'm using it with a computer at home and it's been really cool to be able to monitor (and administer) the computer remotely so easily.

 

Quick question:

I'm monitoring a Windows Server 2012 computer and looking at CPU usage (using the iOS PC Monitor app).  The CPU usage reported in the app seems consistently twice as high as what I see in the Task Manager and Resource Monitor inside of Windows itself.

 

The CPU is an i3-3225, which is dual core, hyper-threaded, and automatically changes its multiplier depending on load (energy saving).  Even though the CPU is rated at 3.3GHz, most of the time it runs at 1.6Ghz because the machine is generally low load.

 

Just curious why I would see differences between Task Manager and PC Monitor as it relates to CPU usage.  Does it have to do with number of threads or on-the-fly multiplier changes?  Oddly, it seems that occasionally if I reboot the Windows computer then PC Monitor reports similar CPU usage (compared to Task Manager) for the duration of that "uptime".  But then I'll reboot again and it'll go back to reporting CPU usage that is twice as high.  So that makes me wonder if it has something to do with PC Monitor initializing itself when the CPU is running at a certain frequency and then "locking" to that frequency, but in reality the CPU changes dynamically?  Any ideas?

 

Thanks in advance!

Aaron

 

[Paul]

Hello,

 

Try rebuilding your performance counters. This has been already discussed here.

 

Rebuild performance counter with these steps:

1. Click Start, and then type cmd in the Start Search box.
2. Right-click cmd in the Programs list, and then click Run as administrator.
If you are prompted for an administrator password or confirmation,
type your password or click Continue
3. At the command prompt, type the following line, and then press ENTER: Lodctr /r
4. You will receive the following message:
"Info: Successfully rebuilt performance counter setting from system backup store"
5. Exit Command Prompt

[aperry01]

Thanks, I think that resolved it.  I had seen that thread earlier, but I thought it was only for situations where the CPU usage wasn't being reported at all.  Thanks for the help!

[aperry01]

Hmmm....this seems to slip back into an incorrect state fairly quickly.