Re: Add iommu device when VM configured with > 255 vcpus
On Tuesday, May 28 2024, Jim Fehlig via Devel wrote:
Hi All,
I vaguely recall a discussion about $subject, but can't find it
now. Perhaps buried in another thread. The topic has been raised
internally again, and I'd like to gauge the community's interest in
automatically adding the necessary devices/config when user has
specified vcpus > 255.
The comparison for prior art is a bit of a stretch, but we e.g. add
<audio type='spice'/> when spice graphics is configured. I know
libvirt has generally tried to avoid policy decisions, but it's not
clear to me where we stand with cases such as this, where every x86 VM
with > 255 vcpus needs a similarly configured iommu.
My two cents here: this is something I would certainly appreciate as a
downstream maintainer of QEMU/libvirt. In fact, I spent part of last
year figuring out and documenting the necessary bits that need to be put
together in order to use more than 288 vCPUs. One of the results of
this effort (with help from David Woodhouse) was:
https://ubuntu.com/server/docs/create-qemu-vms-with-up-to-1024-vcpus
I still have to write the equivalent guide for libvirt, FWIW.
Cheers,
--
Sergio
GPG key ID: E92F D0B3 6B14 F1F4 D8E0 EB2F 106D A1C8 C3CB BF14