I was messing around today with the CPU types that I'm telling QEMU to use.

My home lab is a couple of repurposed Ryzen CPUs:

1 x AMD Ryzen 7 3700X 8-Core Processor (1 Socket)
1 x AMD Ryzen 7 5700G with Radeon Graphics (1 Socket)

I've been looking at the CPU flags available across both CPUs to get the maximum I can out of this install - while still having compatible CPU types to enable live migration.

I threw in the `flags` line in /proc/cpuinfo on both systems into Claude, and it suggested the `EPYC-Rome` CPU type for guests. Turns out the 3700X doesn't have the `xsaves` flag, so it gave me a suggestion of using the following in `/etc/pve/virtual-guest/cpu-models.conf`:

cpu-model: ryzen-cluster-cpu
    reported-model EPYC-Rome
    flags -xsaves
    phys-bits host
    hidden 0

This gives all the features that are common between these CPU types - which also has AES-NI - which `x86-64-v3` doesn't seem to include.

As this seems to be a pretty useful feature to give a 'best case' CPU to the guests, is there a way to do this in PVE without having to go via claude? ie a way to define a 'best capabilities' CPU type for common use between cluster nodes?

Ah, I didn't see that at all.

That being said, I'm struggling to get my head around how it would actually function. I can see how to represent the information I already have - but I'm not sure how I would discover how to create this if I hadn't already used Claude to give me a custom definition.

ie, if I filter based on the 3700X cpu, I don't see the xsaves option - as that CPU doesn't support it - but the 5700G does support it. I can only see xsaves by looking at the CPU flags for the 5700G - where its still set as 'default'.

This seems very counter-productive and very easy to miss things. Even knowing what I was looking for was difficult to achieve.

I wonder if a wizard to add a new CPU definition could be a thing where you can select the nodes you want to make the feature group from, and it picks the closest preset with any custom requirements - such as me using EYPC-Rome - xsaves.

If there's very different CPUs in the cluster, I would expect the common CPU feature set might be greatly reduced - hence the target node selection path for working this out.