High VM-EXIT and Host CPU usage on idle with Windows Server 2025

I've tried to migrate from 2 Windows Server 2025 Core Hyper-V VMs running on Win10 2019 LTSC IoT and Dell E7470 with i5-6300u (2C/4T), 32 GB of RAM, NVMe SSD. The laptop has cooper radiators on SSD, RAM sticks, PTM 7950 on CPU die and it is lifted few centimeters above desk for better air cooling. When Hyper-V is utilized, the cooler starts spinning only on heavy tasks like Windows Updates installation, restarts. Windows host CPU utilization barely reached 3-5% during idle remote session on Hyper-V host.

I converted vhdx images to QCOW2 and created Proxmox VMs. The same VMs running on Proxmox VE utilized int total 4-8% of the CPU. Fan was spinning all the time. Windows VirtIO Drivers were installed. I've tried various Proxmox settings but I gave up few hours later and restored Windows 10 from backup.

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I am afraid we may proceed with Win Sever 2022 instead of 2025 on new infra just for this reason
 
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Ok so hyper-v also does not show any degradation and has the same baseline (between 23h2 and 24h2).

As I think we have collectively tried out every parameter, it is likely that the issue will be a core Qemu issue.

We should try out with vanilla Qemu to see if Proxmox might for example have missed a patch or the problem is in upstream Qemu.
 
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