7:35 p.m.
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>
Now the VM is starting with 2 CPUs. When i try to increase the number of
CPUs i get:
setvcpus dev --guest 4
error: invalid argument: requested vcpu count is greater than the count
of enabled vcpus in the domain: 4 > 2
Strange thing is when i set in the xml file:
<vcpu placement='auto' current='4'>4</vcpu>
the VM starts with 4CPUs and setting the CPUs works.
I can do:
setvcpus dev --guest 2
and:
setvcpus dev --guest 4
Is this a bug? Should i try to upgrade to 1.2.10? There seem to be a lot
of changes in it regarding setvcpus.
thanks and cheers
t.
9:20 p.m.
Am 05.11.14 11:48, schrieb Martin Kletzander:
I'm not quite sure i understand what you mean. What would be a common
use case for this setting? <vcpu placement='auto'
current='2'>4</vcpu>
(unless you have cpu hot(un)plug).
What is neccessary to have that?
thanks and cheers
t.
10:48 p.m.
On 11/05/2014 01:20 PM, Thomas Stein wrote:
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
11:05 p.m.
On 11/05/2014 02:56 PM, Thomas Stein wrote:
In fact, one of the reasons that 'setvcpus --guest' was added in the
guest agent was precisely because direct qemu support for cpu hot-unplug
was not ready yet, and faking things by requiring the guest to do the
work instead of qemu was an attempt to paper around the lack of qemu
support. However, guest unplug is different than qemu unplug on several
fronts; for instance, rebooting the guest will forget what settings the
previous run had been using (that is, libvirt will NOT update XML to
reflect guest settings, because guest interaction is assumed to be
untrusted; while if qemu hot-unplug works, libvirt would update the XML
to match).
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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participants (3)
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Eric Blake -
Martin Kletzander -
Thomas Stein