[libvirt] CPU compare and baseline

[Jiri Denemark]

> Ok, I didn't understand how to use "cpu-baseline", it's not clear in
> the help command.
> So "cpu-baseline" give me the CPU XML file I need to use to be able to
> migrate between two hosts but how I use this XML file ?

You can just stick the output of cpu-baseline to guest's XML file, so you
could have something like the following:

<domain type='kvm'>
  <name>domain-name</name>
  <memory>262144</memory>
  <currentMemory>262144</currentMemory>
  <vcpu>2</vcpu>
  <os>
    <type arch='x86_64' machine='pc-0.12'>hvm</type>
    <boot dev='cdrom'/>
  </os>
  <cpu match='exact'>
    <model>Opteron_G2</model>
    <feature policy='require' name='ht'/>
    <feature policy='require' name='vme'/>
    <feature policy='disable' name='svm'/>
    <feature policy='disable' name='rdtscp'/>
  </cpu>
  ...
</domain>

> Another question, why Libvirt consider CPUs with non-matching vendors
> cannot be compatible ?

That's because CPUs made by different vendors are not generally compatible.
Migration between them may work but it's not guaranteed. Libvirt allows you to
choose whether you want to stick with a single CPU vendor or not. If you put
<vendor> tag into the <cpu> element above, libvirt will forbid migration to a
CPU made by a different vendor. If no <vendor> tag is present, CPU vendor is
not checked during migration.

Jirka