The guest OS does not display the vCPUs added using hotplug

E

emptness

Member
Aug 19, 2022
124
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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?

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The processor cannot be changed at runtime. You would have to restart the VM to apply the changes.
 
emptness said:
Aren't these rules created automatically when installing qemu-guest-agent?
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I have not experienced that and I don't know why you would expect that from the Wiki page.
emptness said:
OS Ubuntu 20.04
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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.
emptness said:
VM options are configured for hotplug.
View attachment 57521
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Maybe sure to enable everything necessary inside the VM for automatic memory hotplug, otherwise the VM sees only 1GB of memory (or less)!
 
Last edited:
leesteken said:
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)!
Click to expand...
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.
 
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