On 1/19/21 1:50 PM, William Herrin wrote:
I haven't used Proxmox but from a 60 second glance through Google that looks like you're asking for nested virtualization. If it works at all, you'd take a double-hit on everything that wants to run in ring 0, a double-hit on virtualized I/O and a double-hit for OS overhead making the result more than a little sluggish. Kinda has "bad idea" written all over it.
KVM, at least, and I think Xen as well, have some features for "shunting" I/O and hypervisor calls through to the bare-metal hypervisor where possible and avoiding double processing and trampolining. It's not nearly as bad as you might think in terms of performance as long as the hardware supports it (nested page tables being the big one). The little I've played with it mostly has proven to be an administrative hassle rather than performance.
I would not recommend mixing and matching hypervisors (e.g. Xen on KVM or vice-versa), though. I'm not even sure you can do so meaningfully, though I bet someone's working on it.
-- Brandon Martin
