Re: [Qemu-devel] [RFC] QMP: add query-hotpluggable-cpus

[David Gibson <david@gibson.dropbear.id.au>]

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On Mon, Feb 15, 2016 at 08:43:41PM +0100, Markus Armbruster wrote:
> Igor Mammedov <imammedo@redhat.com> writes:
> 
> > it will allow mgmt to query present and possible to hotplug CPUs
> > it is required from a target platform that wish to support
> > command to set board specific MachineClass.possible_cpus() hook,
> > which will return a list of possible CPUs with options
> > that would be needed for hotplugging possible CPUs.
> >
> > For RFC there are:
> >    'arch_id': 'int' - mandatory unique CPU number,
> >                       for x86 it's APIC ID for ARM it's MPIDR
> >    'type': 'str' - CPU object type for usage with device_add
> >
> > and a set of optional fields that would allows mgmt tools
> > to know at what granularity and where a new CPU could be
> > hotplugged;
> > [node],[socket],[core],[thread]
> > Hopefully that should cover needs for CPU hotplug porposes for
> > magor targets and we can extend structure in future adding
> > more fields if it will be needed.
> >
> > also for present CPUs there is a 'cpu_link' field which
> > would allow mgmt inspect whatever object/abstraction
> > the target platform considers as CPU object.
> >
> > For RFC purposes implements only for x86 target so far.
> 
> Adding ad hoc queries as we go won't scale.  Could this be solved by a
> generic introspection interface?

That's my main concern as well.

Igor,  did you see my post with a proposal for how to organize
hotpluggable packages of CPUs?  I believe that would also solve the
problem at hand here, by having a standard QOM location with
discoverable cpu objects.

The interface in your patch in particular would *not* solve the
problem of advertising to management layers what the granularity of
CPU hotplug is, which we absolutely need for Power.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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