Re: [libvirt-users] setvcpus libvirt 1.2.9

Eric Blake
Wed, 05 Nov 2014 13:48:38 -0000

On 11/05/2014 01:20 PM, Thomas Stein wrote:
> Am 05.11.14 11:48, schrieb Martin Kletzander:
>> On Wed, Nov 05, 2014 at 11:35:37AM +0100, Thomas Stein wrote:
>>> Hello.
>>>
>>> I'm struggeling a little bit with the setvcpus command. I'm
trying now
>>> to get this running for a linux VM. Here is what i have:
>>>
>>> <vcpu placement='auto'
current='2'>4</vcpu>

This is one case where xen may be a bit more powerful than current qemu
support.  Xen supports booting a guest with a promise of a maximum cpu
larger than what it boots with; but I don't know that qemu does that
well yet.  For now, with qemu, you pretty much have to boot with all
cpus enabled, then after the guest is up and running, disable the cpus
you don't plan to use right away.  CPU hotplug/hot-unplug is still a
work in progress in qemu (for example, some versions of qemu support
hotplug but not hot-unplug).  I haven't played much with it myself to
know what minimum version of libvirt and qemu will do what you want, so
you may have to do some experimentation.

--
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org