[libvirt] Non-contiguous NUMA cell numbers

[Michal Privoznik]

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.

>   </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.
> 

Michal