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



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


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