Windows 2022 - high load on second core (asymmetric)

[Stril]

Hi everyone,

I’m seeing a strange CPU scheduling/load balancing behavior with Proxmox VE 9.1 on Windows Server 2022 Terminal Server VMs.

Environment:

Proxmox VE 9.1
AMD EPYC 9375F hosts
Windows Server 2022 RDS/Terminal Server VMs
Multiple VMs affected
CPU type configured as either:
x86-64-v2-AES
EPYC-Genoa

Problem:

Inside the Windows guests, the second vCPU/core consistently shows noticeably higher load/utilization than all other cores. This happens across multiple VMs and is reproducible.

Interestingly, the issue disappears when I switch the VM CPU type to "host"

With host, CPU utilization is balanced normally across all vCPUs.

However, I would prefer to use an emulated CPU type (x86-64-v2-AES or EPYC-Genoa) because of migration compatibility and cluster flexibility.

What I already checked:

- VirtIO drivers up to date
- Different Multiqueue-values
- NUMA on/off tests
- Different vCPU counts
- Change of vCPU-Profile (NUMAstagic -> Closest)
- With/without VirtIO-RNG device

What confuses me is that I only found forum posts describing the opposite behavior — where host performs worse than generic/emulated CPU types.

Has anyone seen something similar?

Any ideas what could cause the uneven load distribution on the second vCPU specifically?

Thanks!

 

[Sviat]

Hi,

do you have the same CPU load behavior inside the VM, is it the same as you see on PVE side?
What VirtIO drivers installed?
Did you try to assign some older vCPU type to the VM?