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I am testing a .NET application that has advanced GUI capabilities. One specific action takes a long time to complete, up to 5 seconds. While watching the standard Windows Resource Monitor, I noticed that this delay coincides with a severe dip all the way to 0% in the "Maximum Frequency" graph in the Monitor -- see the blue line in the image below.

CPU usage graph in Resource Monitor

Based on the answer to What does the "Maximum Frequency" number mean in the Windows Resource Monitor?, and some other information on the web, my conclusion is that this dip is causing the delay, because the CPU basically is unavailable for about three seconds. Is this the right conclusion? If so, what could cause this dip to happen?

Some information about my setup: this is on a machine running Windows Embedded 7 Standard, running on an Intel Atom E680T processor. All power-saving options are set to maximum performance. The same test does not show this effect on other machines that I tried. Those have more powerful CPU's though.

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    You almost certainly have the cause and effect backwards. The CPU is snoozing because it can't get any work done.
    – David Schwartz
    Commented Oct 16, 2012 at 16:20
  • @DavidSchwartz It turns out that my app was running at Real-Time priority and the Resource Monitor at Normal priority. As a result, the Resource Monitor is scheduled out for a while and not capable of displaying the correct values for Maximum Frequency. Is that similar to what you are describing in your comment?
    – Reinier Torenbeek
    Commented Oct 16, 2012 at 18:47
  • Nope, that wasn't what I was thinking at all. But that's actually pretty funny.
    – David Schwartz
    Commented Oct 16, 2012 at 18:50

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The answer to my question is: the Maximum Frequency does not dip, even though the Resource Monitor indicates it does.

My process was running at Real-Time Priority, while the Resource Monitor was running at Normal Priority. As soon as my process got really busy, the Resource Monitor was not granted the CPU cycles required to measure the values it was monitoring. As a "consequence", it erroneously displayed zero values.

One thing that surprises me in particular is the fact that the GUI of the Resource Monitor was happily updating, the graph shifted leftwards without any noticeable irregularities. The cause would have been much easier to identify if the GUI would have stalled as well.

Sorry for answering my own question -- not sure whether this is an appropriate thing to do. I do not want other people to spend time on this in vain either though.

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