Re: [Qemu-devel] [PATCH v4 0/9] enable numa configuration before machine_init() from QMP

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Apr 17, 2018 at 04:13:34PM +0200, Markus Armbruster wrote:
> Igor Mammedov <imammedo@redhat.com> writes:
> 
> [...]
> > Series allows to configure NUMA mapping at runtime using QMP
> > interface. For that to happen it introduces a new '-preconfig' CLI option
> > which allows to pause QEMU before machine_init() is run and
> > adds new set-numa-node QMP command which in conjunction with
> > query-hotpluggable-cpus allows to configure NUMA mapping for cpus.
> >
> > Later we can modify other commands to run early, for example device_add.
> > I recall SPAPR had problem when libvirt started QEMU with -S and, while it's
> > paused, added CPUs with device_add. Intent was to coldplug CPUs (but at that
> > stage it's considered hotplug already), so SPAPR had to work around the issue.
> 
> That instance is just stupidity / laziness, I think: we consider any
> plug after machine creation a hot plug.  Real machines remain cold until
> you press the power button.  Our virtual machines should remain cold
> until they start running, i.e. with -S until the first "cont".
> 
> I vaguely remember me asking this before, but your answer didn't make it
> into this cover letter, which gives me a pretext to ask again instead of
> looking it up in the archives: what exactly prevents us from keeping the
> machine cold enough for numa configuration until the first "cont"?

I also think this would be better, but it seems to be difficult
in practice, see:
http://mid.mail-archive.com/20180323210532.GD28161@localhost.localdomain

-- 
Eduardo