4

Do power settings in the actual VMs affect performance of the virtual machines?

Improve this question

2 Answers 2

Reset to default
5

The only power management exposed to the guest VM involves processor idling states. Changing the power policy within the guest can influence how often the guest puts its virtual processors into these idle states. So, yes, you can affect the guest's performance via power settings.

With that said, you won't be able to affect the performance by much, as these idle states are only really used when there isn't any work to do. The amount by which you might affect the scheduler running within the guest is probably swamped by the effect of the hypervisor scheduling the virtual processors.

When running one VM with a constant CPU load, I would expect no measurable difference based on guest power settings. When running lots of VMs with bursty loads, changing power settings within a guest could cause it to use more CPU time than it really needs, which might cause the other VMs to suffer somewhat.

Improve this answer
1

Yes, on the client Hyper-V versions up to Windows 8, I've noticed that the frequency reported in Task Manager did not accurately reflect the actual CPU frequency or power consumption of the device (tested via micro benchmarks or an external power monitor). That said, the power settings in the Power Options control panel did affect the performance of the host OS and VMs.

On Windows Server, not as many power options are exposed, but the effect is the same: a down-throttled CPU will reduce the performance of the host OS and any VMs running on the server.

Improve this answer
2
  • This sounds like you're saying that Power settings in the VM can override the Host OS, which is incorrect. The Host OS will assign less runtime to VMs that choose idle states, but that really affect the Host OSes power states.
    – Chris S
    Jul 22, 2013 at 16:37
  • 1
    Oh shoot, I misread the question asker. You are correct, and I wrote my answer regarding power settings on the host OS affecting the guests, not guests affecting other guests. AFAIK, power settings on guests should not affect anything else, unless as you say, the power settings change how the guest uses the CPU (how it allocates threads on processors, how it sets power states on its devices and the CPU, etc.)
    – Aaron Friel
    Jul 22, 2013 at 18:21

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .