On a fresh install of Windows Server 2012 R2 in a Hyper-V host role, with four VMs running but idle and nothing going on in any of the VMs or on the host, I get a periodic CPU spike on a regular periodic basis (about every 12 seconds). The process that's generating the spike, per Task Manager on the host machine, is vmms.exe. The spike are pretty severe, lasting a few seconds and using close 80-100% of one core. What would be causing this? How can I diagnose it (i.e. other than knowing that it's vmms.exe)?


Periodic CPU spikes from VMMS indicate that you're running some monitoring tool that is polling information about the VMs. This could be the Hyper-V manager, System Center Virtual Machine Manager, etc.

  • +1 I might explicitly mention that vmms is the process in the host OS that manages/communicates with the Hyper-V kernel. So it's probably something monitoring the VMs, but could conceivably be periodic changes being made to the VMs or similar. – Chris S Apr 22 '14 at 20:56
  • I too thought it might be come monitoring or polling process, but I'm not running anything else on the machine (and I know there is no remote monitoring going on). In fact, I shut down all the VMs, and with nothing running in the foreground at all except Task Manager, I still get the spikes (which are each several seconds long and take up 80-100% of one CPU core--which would be very heavy for a monitoring process anyway). Is there any way to "debug" vmms (without source code, of course) to find out what's calling it? Are there any logs from vmms (or can it be made to produce some logs)? – eric Apr 23 '14 at 1:13

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