Re: [Xen-users] Issues with vcpu-set

[Anthony PERARD <anthony.perard@citrix.com>]

On Wed, Jan 29, 2014 at 10:11:44AM +0000, Ian Campbell wrote:
> On Tue, 2014-01-28 at 18:44 -0700, Yun Wang wrote:
> > Sorry for the so late reply.
> > I had this issue in Xen-4.3.0 (official release) and Xen-4.4.0-rc1-25-g9a80d50
> 
> And are you using the version of qemu-xen which ships with those
> releases or your own version, perhaps from upstream?
> 
> ISTR that vcpu hotplug for HVM guests was missing from qemu-xen in Xen
> 4.3.x but I thought it had been added during the 4.4.x development
> cycle. Adding Anthony + xen-devel to confirm.

We've added vcpu hotplug to our tree in Xen 4.3.

QEMU upstream is able to do vcpu hotplug with Xen only with the last
release, 1.7. The two previous release (1.5 and 1.6) miss two patches,
and any QEMU release before that those not support cpu hotplug.

> > Here is the /var/log/xen/
> > Waiting for domain centos65.pv (domid 1) to die [pid 8116]
> > 
> > 
> > Here is the output of "xl -vvv vcpu-set"
> 
> Is this from 4.3 or 4.4? I think at this point we should focus on the
> issue with 4.4.
> 
> I also asked for your guest cfg file -- please can you show it to us.
> 

[...]

> > libxl: debug: libxl_qmp.c:555:qmp_send_prepare: next qmp command: '{
> >     "execute": "cpu-add",
> >     "id": 2,
> >     "arguments": {
> >         "id": 0
> >     }
> > }
> > '
> > libxl: debug: libxl_qmp.c:299:qmp_handle_response: message type: error
> > libxl: error: libxl_qmp.c:289:qmp_handle_error_response: received an
> > error message from QMP server: Not supported

This right here means that xl support vcpu-set with qemu-xen, but the
QEMU used does not.

> > On Tue, Oct 1, 2013 at 3:24 AM, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> > > On Mon, 2013-09-30 at 10:52 -0600, Yun Wang wrote:
> > >> Hi all,
> > >>
> > >> I tried to use "xl vcpu-set" to change the vCPU number of VMs in Xen
> > >> 4.4-unstable and had the following errors.
> > >
> > > What was the full command line which you used?
> > >
> > > Which exact version of 4.4-unstable (i.e. git commit) were you using?
> > >
> > >> libxl: error: libxl_qmp.c:289:qmp_handle_error_response: received an
> > >> error message from QMP server: Unable to add CPU: 0, it already
> > >> exists.

This is just a message that I don't know how to remove.

Since libxl does not know which cpu are already plugged-in, it asks QEMU
to plug every asked cpu. QEMU just reply back as an error that some CPU
are already plugged. And libxl does print every error that QEMU send.

-- 
Anthony PERARD