The guest OS does not display the vCPUs added using hotplug

[emptness]

Hello everyone!
I'm testing adding a cpu without restarting the VM.
The guest OS does not display the added vCPUs.
What could be the matter? Is this a bug?

 

[fschauer]

The processor cannot be changed at runtime. You would have to restart the VM to apply the changes.

 

[leesteken]

The number of VCPUs can be changed at runtime, but did you setup hot-plug inside the VM and enable hot-plug for CPU in VM, Options, Hotplug? See https://pve.proxmox.com/wiki/Hotplug_(qemu_disk,nic,cpu,memory). And does the operating system inside the VM support CPU hot-plug?

 

[emptness]

The number of VCPUs can be changed at runtime, but did you setup hot-plug inside the VM and enable hot-plug for CPU in VM, Options, Hotplug? See https://pve.proxmox.com/wiki/Hotplug_(qemu_disk,nic,cpu,memory). And does the operating system inside the VM support CPU hot-plug?

Aren't these rules created automatically when installing qemu-guest-agent?
OS Ubuntu 20.04
VM options are configured for hotplug.

 

[leesteken]

Aren't these rules created automatically when installing qemu-guest-agent?

I have not experienced that and I don't know why you would expect that from the Wiki page.

OS Ubuntu 20.04

I needed to add it myself for Ubuntu with qemu-guest-agents installed and active. Which kernel modules and parameters and/or udev rules are necessary (inside the VM) depend on the exact kernel version inside your Ubuntu VM.

VM options are configured for hotplug.
View attachment 57521

Maybe sure to enable everything necessary inside the VM for automatic memory hotplug, otherwise the VM sees only 1GB of memory (or less)!

 

[emptness]

I have not experienced that and I don't know why you would expect that from the Wiki page.

I needed to add it myself for Ubuntu with qemu-guest-agents installed and active. Which kernel modules and parameters and/or udev rules are necessary (inside the VM) depend on the exact kernel version inside your Ubuntu VM.

Maybe sure to enable everything necessary inside the VM for automatic memory hotplug, otherwise the VM sees only 1GB of memory (or less)!

Thank you for your advice.
The rule SUBSYSTEM=="cpu", ACTION=="add", TEST=="online", ATTR{online}=="0", ATTR{online}="1" helped. Now the number of processors is changing inside the VM.
By the way, RAM expands without problems. No additional actions were required inside the VM.