vCPU value is wrong and not adjustable

[cognitionis]

Hello everyone,
I have the following CPU:
AMD Ryzen 9 6900HX processor (8C/16T, 3.8GHz up to 4.9GHz)

So it should be possible to select 16 vCPUs in the settings of the VM with 8 cores, since 1vCPU=1 thread.
But I can only select 8vCPUs with 8 cores, why is that?

And I have tried numerous workarounds in the meantime.
1) NUMA on, NUMA off.
2) I manually adjusted the config in Proxmox using the console and the command nano /etc/pve/qemu-server/100.conf and manually set the vCPUS to 16. After that I could no longer start the VM with Windows and only received error messages
3) Checked BIOS config
4) Display the config in Proxmox Terminal using lscpu. There, threads per core are correctly shown as 2
5) Changed CPU type to "host" in the VM config
6) Probably further checks.

In any case, I can't find the error and don't understand how I can now configure Proxmox or the VMs correctly so that I can properly distribute my performance to the respective VMs

Please help!

Thank you in advance!

greetz

 

[Neobin]

But I can only select 8vCPUs with 8 cores, why is that?

In Proxmox VE the maximal number of plugged CPUs is always cores * sockets. To start a VM with less than this total core count of CPUs you may use the vcpus setting, it denotes how many vCPUs should be plugged in at VM start.

https://pve.proxmox.com/pve-docs/chapter-qm.html#_vcpu_hot_plug

[0] https://pve.proxmox.com/wiki/Hotplug_(qemu_disk,nic,cpu,memory)

 

[cognitionis]

Hello,
thanks for the answer.
Maybe I described my problem badly, but my problem is not setting fewer vCPUs, but more, and I have a maximum limit here that I can't get around. Ultimately, the following should be possible.
My assumption is 1 vCPU = 1 thread
Option 1) VM with 8 cores and 16 vCPUs --> Cannot be set because 8 vCPUs is the maximum
Option 1) VM with 4 cores and 8 vCPUs --> Cannot be set either because 4 vCPUs is the maximum

I hope I was able to illustrate it better with the two options.

Thank you in advance!

 

[BobhWasatch]

Your assumption is incorrect. The vCPU setting has to do with CPU hotplug. It is the number of cores the machine will start with, then you can hot-plug up to the number in the upper section of that dialog. From the Proxmox Manual (linked at the top of the web GUI in PVE):

vCPU hot-plug​

Modern operating systems introduced the capability to hot-plug and, to a certain extent, hot-unplug CPUs in a running system. Virtualization allows us to avoid a lot of the (physical) problems real hardware can cause in such scenarios. Still, this is a rather new and complicated feature, so its use should be restricted to cases where its absolutely needed. Most of the functionality can be replicated with other, well tested and less complicated, features, see Resource Limits.

In Proxmox VE the maximal number of plugged CPUs is always cores * sockets. To start a VM with less than this total core count of CPUs you may use the vcpus setting, it denotes how many vCPUs should be plugged in at VM start.

ETA: @Neobin said essentially the same thing in different words.