Could not change "-machine" by 'xe vm-param-set'

lyan

With default xcp-ng 8.2, I saw the hvm is created with "qemu-dm-3 -machine pc-0.10,accel=xen,"

I checked xe vm-param-setthat there is no such option change "-machine", I tried "other-config" got no such key error.

I am new to xcp-ng, wondering if there is a way to change the machine model for qemu, such as "pc-i440fx-42".

Thanks.

olivierlambert

Hi,

You can't change that in XCP-ng. Can you tell us what do you want to achieve?

lyan

Thanks for the reply, @olivierlambert. I recently hit a bug that Xen could not create msi interrupt for HVM, I noticed that we qemu-dm is using pc-0.1 as the machine model by default, as the starter, I kind of want to change it to i440fx-4.2 which is aligned to the qemu version. I can not change it from the cmd line atm, maybe it is hard-wired in the code?

olivierlambert

I think it's slightly more complicated than that. Adding @ThierryEscande in the loop

ThierryEscande

Hi @lyan,

This might be related to a known issue about PCI passthrough with nvme devices: the kernel tries to allocate more MSI-X vectors than the guest can handle. You can try to increase the number of guest IRQs with the Xen boot parameter extra_guest_irqs. The default is 64 and you can increase it to 128 with:

/opt/xensource/libexec/xen-cmdline --set-xen "extra_guest_irqs=128"

A reboot of the host is needed.

lyan

Hi, @ThierryEscande, thanks for the input here。

It is pretty interesting that I kind also located the same place by following the interrupter path.
https://github.com/liayan/xen-xcp-ng/blob/main/xen/common/domain.c#L250

It quite fits our case atm that issues happened after hitting the limit of 64. Unfortunately, I can not test it yet because our host is stuck in a weird POST status. Will update here later.