[libvirt] [RFC] Data in the <topology> element in the capabilities XML

[Peter Krempa]

Hi everybody,

a while ago there was a discussion about changing the data that is 
returned in the <topology> sub-element:

<capabilities>
   <host>
     <cpu>
       <arch>x86_64</arch>
       <model>SandyBridge</model>
       <vendor>Intel</vendor>
       <topology sockets='1' cores='2' threads='2'/>


The data provided here is as of today taken from the nodeinfo detection 
code and thus is really wrong when the fallback mechanisms are used.

To get a useful count, the user has to multiply the data by the number 
of NUMA nodes in the host. With the fallback detection code used for 
nodeinfo the NUMA node count used to get the CPU count should be 1 
instead of the actual number.

As Jiri proposed, I think we should change this output to separate 
detection code that will not take into account NUMA nodes for this 
output and will rather provide data as the "lspci" command does.

This change will make the data provided by the element standalone and 
also usable in guest XMLs to mirror host's topology.

The meaning of the attributes of that element isn't really documented 
anywhere, so as an additional precaution we should document that.

( http://libvirt.org/formatcaps.html )


For some additional background, please refer to the original discussion 
here:
https://www.redhat.com/archives/libvir-list/2012-March/msg01123.html

Thanks in advance for your comments and suggestions.

Peter