[SOLVED] Windows guests are extremely slow

ProfessionalN00b

New Member
May 21, 2025
28
4
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Estonia
Hello

I came from Hyper-V last month where my VMs performed very well. The host server is the same, so I expected the same performance from a different hypervisor as well.

Is there some sort of best practice for Windows guests? That is current. I tried to follow whatever suggestions I could find on YouTube, but clearly none of it has helped.

This is a config of a domain controller VM:
Code:
agent: 1
balloon: 2048
bios: ovmf
boot: order=scsi0
cores: 6
cpu: host,flags=+hv-evmcs;+aes
efidisk0: Storage:vm-100-disk-0,efitype=4m,pre-enrolled-keys=1,size=4M
machine: pc-q35-9.2+pve1,viommu=virtio
memory: 4096
meta: creation-qemu=9.2.0,ctime=1747927001
name: myVMname
net0: virtio=00:00:11:0D:00:17,bridge=vmbr0,tag=2
numa: 0
onboot: 1
ostype: win10
scsi0: Storage:vm-100-disk-2,backup=0,iothread=1,size=60G
scsihw: virtio-scsi-single
smbios1: uuid=0007f5b5-000c-0003-8000-bc739459000b
sockets: 1
startup: order=1
tags: dc;win
tpmstate0: Storage:vm-100-disk-1,size=4M,version=v2.0
vcpus: 1
vmgenid: 28498000-2000-4500-000d-673ac4000063

Let me know if I need to include something else.
---
Edit: I thought maybe adding more cores would help so I increased core count from 4 to 6 yesterday and added the cpu flags, it had no effect.
 
Last edited:
i understand that you don't want to disable VBS but if you struggle with performance then that's most likely the culprit.

https://forum.proxmox.com/threads/t...-of-windows-when-the-cpu-type-is-host.163114/
I changed the processor type from Host to x86-64-v2-AES. Reduced core count to 4 again and the performance is now at expected levels, but now VBS is enabled, but not running, which is not ok. Not only doesn't Proxmox support Kernel DMA, now I can't use VBS either.

I'm complaining because the performance degradation wasn't nearly as bad on Hyper-V with VBS. I understand that the real problem here is the older CPU. I've heard that performance drop can be up to 30% with mitigations, but I'm experiencing way above 50 with VBS enabled (which requires the Host processor type). It was only slightly better than a slideshow.
Can't go back to Hyper-V either because 2019 was the last free version.

I guess case closed :(