Hyper-V host CPU utilization no longer reflects VM load — shows near-idle even when VMs are pegged at 100%
Anyone else run into this after a Windows update a few months back? My Hyper-V host CPU in Task Manager shows ~2% utilization no matter what my VMs are doing. A few months back it felt accurate — if a VM was under load, you'd see it on the host. Now it's completely disconnected.
To reproduce it, I wrote a Python script to max out every vCPU on a guest VM. htop inside the VM confirms all cores pinned at 100% (see screenshot — 12 threads running, load average 6.15). Meanwhile, the host Task Manager barely moves. The host is an Intel Xeon Gold 6526Y with 32 logical processors and 128GB RAM, so it's not a resource ceiling issue.
My theory is that a Windows update changed how Hyper-V reports guest CPU activity to the host's performance counters, or something shifted in the hypervisor scheduling layer. The VM is clearly doing real work — the host just stopped caring to report it.
Has anyone found a fix or rollback path? I'd rather not start bisecting months of cumulative updates blind.