[libvirt] Non-contiguous NUMA cell numbers

[Andrea Bolognani]

Hi all,

libvirt currently doesn't allow you to configure a guest with something
like

  <cpu>
    <topology sockets='2' cores='5' threads='8'/>
    <numa>
      <cell id='0' cpus='0-39' memory='1048576' unit='KiB'/>
      <cell id='16' cpus='40-79' memory='1048576' unit='KiB'/>
    </numa>
  </cpu>

with the following error:

  XML error: Exactly one 'cell' element per guest NUMA cell allowed,
  non-contiguous ranges or ranges not starting from 0 are not allowed

The error message is very specific about not allowing gaps in NUMA cell
numbering; however, on the very same host, I have

  $ numactl --hard | head -1
  available: 4 nodes (0-1,16-17)

so gaps in numbering are definitely possible, at least on ppc64.

Should we consider relaxing this requirement and allow
arbitrarily-numbered NUMA cells? Is there a specific reason why it was
forbidden in the first place?

Cheers.

-- 
Andrea Bolognani
Software Engineer - Virtualization Team