Terrible Windows 10 VM performance on Proxmox

[carminefox]

Hi everyone, I've had a Windows VM on Proxmox for about 3-4 months. I've always had terrible performance. The problem is I absolutely cannot reformat this VM as it's very important and has software that I can't reinstall on a clean VM. It also has a vGPU passthrough, but the VM is extremely slow; it takes 10-15 seconds to open File Explorer or 1-2 minutes to open the "Photos" app.

This is my config:

agent: 1
args: -uuid 00000000-0000-0000-0000-000000000119 -cpu host,kvm=off
bios: ovmf
boot: order=virtio0;net0
cores: 8
cpu: kvm64,hidden=1,flags=+pcid
efidisk0: local-lvm:vm-110-disk-0,efitype=4m,pre-enrolled-keys=1,size=4M
hostpci0: 0000:08:00.0,mdev=nvidia-243
machine: pc-q35-9.2+pve1
memory: 16384
meta: creation-qemu=9.2.0,ctime=1751138092
name: windows
net0: virtio=BC:54:31:6B:1A:54,bridge=vmbr0,firewall=1,tag=20
numa: 0
ostype: win10
scsihw: virtio-scsi-single
smbios1: uuid=
sockets: 1
virtio0: local-lvm:vm-110-disk-1,cache=writeback,iothread=1,size=99840M
vmgenid

I also tried the Host CPU but it's still extremely slow. I have a server with two Xeon(R) CPU E5-2680 v4 processors.

 

[SteveITS]

try x86-64-v3-AES or x86-64-v2-AES as the CPU.

G

Post in thread 'CPU type `host` is significantly SLOWER than `x86-64-v2-AES`'

Mar 5, 2025

I am shocked to discover what seems absolutely counter-intuitive to me, but maybe someone can explain me?

I have a stock Win11 24H2 and I initially set it up with x86-64-v2-AES and it was zipping along as one would expect.

View attachment 79185

[...]
View attachment 79189

And one more sanity test, I powered down. Set back to "x86-64-v2-AES" and it's zippy fast again. ?!?!?

First pic x86-64-v2-AES : Windows detects VM (Virtual machine = Yes) so no nested Hyper-V running (required for VBS )
Second pic "host" : Windows doesn't detect VM ( Virtualisation = Enabled )...

• _gabriel

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