(missing) HyperV in guest CPU usage

[Dominik-esb]

Problem Statement

Currently there is no way to get a Taskmgr like CPU utlliization for hyper-v VM in guest.

We have following metrics availible:

windows_hyperv_hypervisor_virtual_processor_mode_time_total	Time that processor spent in different modes (hypervisor, guest_run, guest_idle, remote)	counter	vm, core, state
windows_hyperv_hypervisor_virtual_processor_run_time_total	Time that processor spent	counter	vm, core 

I didnt find a way to calculate the in guest usage with this metrics.

Proposed Solution

I remember an issue some more time ago. It was about the windows CPU metrics and resulted in this new way to measure windows cpu util:

sum by (instance) (
  clamp_max(
    (
      rate(windows_cpu_processor_utility_total{
        job=~"$job",
      }[1m])
      /
      rate(windows_cpu_processor_rtc_total{
        job=~"$job",
      }[1m])
    ), 100
  )
) 

Maybe we can implement something for the in guest cpu usage.

I know hyper-v can report in guest metrics via the Measure-VM powershell command and also Windows admin center reports vm cpu metrics but I had no luck to find a winapi that help receiving this metrics.

Additional information

Maybe someone can help me find a way?

I want to use this place here to document my findings.

Acceptance Criteria

• In guest vm CPU metric

[jkroepke]

If you go into perfmon, you may see the Performance Counter as formatted value. Does that fit?

[Dominik-esb]

Observations

Hyper-V Performance Counters

• \Hyper-V Hypervisor Logical Processor(_Total)\% Total Run Time
• \Hyper-V Hypervisor Virtual Processor(_Total)\% Total Run Time

Formula:

run_time / busy_time * 100

Limitations:

• Host-level only
• Aggregated across VMs
• Not accurate for per-VM usage

---

Per-VM Approximation

\Hyper-V Hypervisor Virtual Processor(<VM>:Hv VP X)\% Total Run Time

Averaging all VPs per VM gives ~±10% accuracy compared to Task Manager.

---

Root Cause of Inaccuracy

Hyper-V uses scheduler time, not actual performance.

Modern CPU usage (Task Manager) uses:

• APERF
• MPERF

real_frequency = base_frequency * (APERF_delta / MPERF_delta)

This accounts for Turbo Boost, power saving, and throttling.

As HyperV does no populate any Virtual Processor metrics witch take the frequency into calculation, we'll be limited to the ~±10% accuracy of \Hyper-V Hypervisor Virtual Processor.