Re: [Qemu-devel] [PATCH x86-next v2] target-i386: add PCID flag to Westmere, Sandy Bridge and Ivy Bridge

[Vincent Bernat <vincent@bernat.im>]

 ❦ 16 janvier 2018 10:41 -0200, Eduardo Habkost <ehabkost@redhat.com> :

>> > Adding Westmere-PCID would require adding a Westmere-PCID-IBRS
>> > CPU model too, so this is starting to look a bit ridiculous.
>> > Sane VM management systems would know how to use
>> > "-cpu Westmere,+pcid" without requiring new CPU model entries in
>> > QEMU.  What's missing in existing management stacks to allow that
>> > to happen?
>> 
>> That's what I actually do. So, I am fine with the solution of doing
>> nothing. However, it would be nice for unaware people to get the speedup
>> of pcid without knowing about it. Maybe we can just forget about
>> Westmere and still apply it to Sandy Bridge and Ivy Bridge.
>
> If management stacks today don't let the user choose
> "Westmere,+pcid", we probably have no other choice than adding a
> Westmere-PCID CPU model.  But our management stacks need to be
> fixed so we won't need similar hacks in the future.

With libvirt:

  <cpu mode='custom' match='exact'>
    <model>Westmere</model>
    <feature policy='require' name='pcid'/>
  </cpu>

We are using CloudStack on top of that and it's also an available
option. However, looking at OpenStack, it doesn't seem possible:
 https://github.com/openstack/nova/blob/6b248518da794a4c82665c22abf7bee5aa527a47/nova/conf/libvirt.py#L506
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