[libvirt] Non-contiguous NUMA cell numbers

[Andrea Bolognani]

n Mon, 2016-01-04 at 07:57 +0100, Michal Privoznik wrote:
> On 23.12.2015 17:14, Andrea Bolognani wrote:
> > 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>
> 
> This says you are configuring GUEST NUMA nodes, and last time I checked
> qemu did not support non-continuous NUMA nodes. So, whatever your HOST
> topology is, in GUEST you want NUMA nodes to be continuous.

I checked again and, as you and Daniel suggested, QEMU does not support
non-contiguous NUMA nodes, eg.

  qemu-kvm                                   \
    -m 2048                                  \
    -smp 80,sockets=2,cores=5,threads=8      \
    -numa node,nodeid=0,cpus=0-39,mem=1024   \
    -numa node,nodeid=16,cpus=40-79,mem=1024

outputs

  qemu-kvm: numa: Node ID missing: 15

so indeed there's a very good reason for libvirt to reject that NUMA
configuration.

Cheers.

-- 
Andrea Bolognani
Software Engineer - Virtualization Team