[libvirt] [PATCH 3/3] virCaps: Expose distance between host NUMA nodes

[Daniel P. Berrange]

On Mon, Jun 02, 2014 at 02:16:00PM +0200, Michal Privoznik wrote:
> If user or management application wants to create a guest,
> it may be useful to know the cost of internode latencies
> before the guest resources are pinned. For example:
> 
> <capabilities>
> 
>   <host>
>     ...
>     <topology>
>       <cells num='2'>
>         <cell id='0'>
>           <memory unit='KiB'>4004132</memory>
>           <cell id='0' distance='10'/>
>           <cell id='1' distance='20'/>

I'd be a little more comfortable if we didn't use a <cell>
within a <cell>. Perhaps lets use 'sibling' as the name
instead and group the elements. eg could we do

  <distances>
     <sibling id="0" value="10"/>
     <sibling id="1" value="20'/>
  </distance>

>     </topology>
>     ...
>   </host>
>   ...
> </capabilities>
> 
> we can see the distance from node1 to node0 is 20 and within nodes 10.

One thing with having the data under each <cell> is that we're
actually reporting twice as much as we need to. ie the distance
between cell N and M is reported under both N and M. A different
option would be todo reporting at the toplevel within <topology>
eg

 <distances>
    <siblings distance="10">
       <cell id="0"/>
       <cell id="1"/>
    </siblings>
 </distance>

I'm not sure whether doing this is worth while or not though ?

Regards,
Daniel
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