Windows 10 VMs consume too much CPU usage while being idle

This seems to be an issue with KVM virtualisation.

• I deployed windows VMs on an unused hypervisor host
• I assigned 4 cores and 50 GB RAM to it

I notice the following:

• inside the VM I see task manager showing 1% CPU usage and 1.2 GB RAM usage
• on the hypervisor host I see the qemu process consuming 70% to 240% CPU usage and 50GB RAM

Possible tweaks to improve the situation

• In the VM install virtio ballooning, network and block drivers, and install the qemu-guest-agent too as described here
• Make sure the qemu-guest-agent is running after rebooting the VM (run the powershell command Get-Service QEMU-GA)
• In opennebula template turn the feature "qemu guest agent" on

  FEATURES = [
    ACPI = "yes",
    APIC = "yes",
    GUEST_AGENT = "yes",
    HYPERV = "yes" ]
  

• In opennebula template turn on the ballooning autodeflate feature and a couple of hyperv tweaks

  RAW = [
    DATA = "<features><hyperv> <synic state='on'/> <stimer state='on'/> </hyperv></features>
            <devices> <memballoon model='virtio' autodeflate='on' /> </devices>",
    TYPE = "kvm" ]
  

• Change the disk device of the windows VM to "virtio" driver; might need a couple of tweaks to reboot from the new drive
• Change the network device of the windows VM to "netkvm" driver
• OpenNebula unfortunately does not support yet setting two different memory sizes, so that the balloon gets inflated/deflated. See issues 949 and 906
  • so there doesn't seem to be a way to reduce the 50GB RAM utilisation
  • we can minimize the impact by keeping a big swap partition per SSD drive on the hypervisor hosts
  • and by running services "ksm" and "ksmtuned" on the hypervisor hosts (kernel same page merging, see here)

tips

• Test if the hypervisor connects to the qemu-guest-agent:
  • run virsh dumpxml $DOMAINID
  • check the status "connected" in a line like the following:
  • <target type='virtio' name='org.qemu.guest_agent.0' state='connected'/>
• You can also get information with:

  virsh qemu-agent-command $DOMAINID '{"execute":"guest-info"}'

resources

• virtio windows drivers and qemu-guest-agent
• libvirt docs for memballoon
• VirtIO Memory Ballooning, pretty up to date post
• OpenNebula template configuration docs