About idle CPU utilization on windows 11

[bellocarico]

I'll try to keep this as short as possible but some historical context is needed to explain what my issue is and what I incidentally discovered.

For months (since installation really) I had both my servers on Proxmox v7 with one Windows11 VM each. Both VMs are installed with the qemu agent (9th Jan 2023 release) and both using about 20-24% of CPU while idle. CPU seen from the Proxmox side, not via task manager.

This week I performed in order:
- upgraded of the qemu agent to 19th Sept 2023 release
- upgraded of proxmox from 7 to 8
- after reading up on windows cpu usage in idling: changed VM type from win11 to Other

Result:
- Server 1 the upgrade didn't work (same identical server HW as Server2) I could however notice that with the VM type Other the CPU for the Win11 VM went town where it's expected to be while idling so 3-5%, the other server that up
- Server 2: the upgrade was completed successfully the Win11 VM CPU stayed at 20-24% despite the VM type change to Other.

I have tried to fiddle further with Server 2's Win11 VM parameters but I could just not bring down the CPU like on Server 1.

Incidentally this morning I have fixed the upgrade issue on Server 1 and went fully to v8 (befofe it was a partial upgrade only). As soon as this was completed the Win11 VM reported CPU went back to 20% idling :-(

That's pretty much where I am now. Unable to bring down the CPU usage for Windows 11 VMs under 20% despite the fact that they do absolutely nothing.

Admittedly the HW is old but the fact that I was able to fix this on v7 somehow makes me hope I'm just missing something minor.

Any tip/help please?
Thanks

 

[bellocarico]

I'm progressing on this topic:

For Windows VM it helps to add the -no-hpet after args: in the $VM.conf this brought down the usage to about 0-10%



however I'm expecting this to be even lower... like 3% or something as it used to be long time ago. Out of all the reading I did on this topic I tried but with no visible result to switch the chipset to i440fx and disabled all the unused USB root from within the OS.

I also tried all the CPU on a single socket (I have a dual CPU motherboard) and also the CPU type: kvm64. These operations specifically changes nothing in terms on CPU usage.

There's certainly still something missing here, but I really would like to bring this down to where it was before. Anything else I could try please?

Thanks!

 

[Boerny41]

Hi there,

My Windows VM was behaving the same way, constantly staying at 20-30% CPU load in idle. Setting -no-hpet, or in my case setting the guest OS to "other" (should do the same thing) got it down to ~12%, but I'm still getting annoying jumps. Like every 6 seconds it jumps up to 30% and back down to 10%.

Also, I feel like 12% idle CPU usage is too much for what the server is doing. Have you managed to tweak it further?

 

[bellocarico]

Hi there,

My Windows VM was behaving the same way, constantly staying at 20-30% CPU load in idle. Setting -no-hpet, or in my case setting the guest OS to "other" (should do the same thing) got it down to ~12%, but I'm still getting annoying jumps. Like every 6 seconds it jumps up to 30% and back down to 10%.

Also, I feel like 12% idle CPU usage is too much for what the server is doing. Have you managed to tweak it further?

I have two servers (standalone) both with windows 11 VMs running the latest version of virtio and pretty much the same config.
So hot plug disaed, balooning disables, numa enabled, use tablet for pointer disabled, etc





The second VM is identical but has a single NIC and no GPU pass though.

In the past VM1 had high CPU like and VM2 was within limit (2-5%), now checking it's opposite, VM1 ranges 2-5% and VM2 it's min 10%. Go figure.

You can try repairing windows first, then virtio and see how it goes but don't quote me , I feel like this is mostly random or driven by an event I'm unable to identify.