Kvm Windows Timer for High Idle Cpu

August 17, 2021

For windows newer than 1803, it would have a high CPU on host (20%) even when the guest CPU is idle. It needs the following Hyper-V Enlightenments. https://github.com/qemu/qemu/blob/master/docs/hyperv.txt

<hyperv>
    <synic state='on'/>
    <stimer state='on'/>
</hyperv>

The end xml:

<hyperv>
  <relaxed state='on'/>
  <vapic state='on'/>
  <spinlocks state='on' retries='8191'/>
  <synic state='on'/>
  <stimer state='on'/>
</hyperv>

These should be the default setting when create the vm from vm-manager. Keep here for reference.

<clock offset='localtime'>
   <timer name='rtc' tickpolicy='catchup'/>
   <timer name='pit' tickpolicy='delay'/>
   <timer name='hpet' present='no'/>
   <timer name='hypervclock' present='yes'/>
 </clock>

Reference: https://bugzilla.redhat.com/show_bug.cgi?id=1610461