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

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

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On Tue, Feb 23, 2016 at 06:26:20PM -0300, Eduardo Habkost wrote:
> On Tue, Feb 23, 2016 at 10:46:45AM +0100, Igor Mammedov wrote:
> > On Mon, 22 Feb 2016 13:54:32 +1100
> > David Gibson <david@gibson.dropbear.id.au> wrote:
> [...]
> > > This is why Eduardo suggested - and I agreed - that it's probably
> > > better to implement the "1st layer" as an internal structure/interface
> > > only, and implement the 2nd layer on top of that.  When/if we need to
> > > we can revisit a user-accessible interface to the 1st layer.
> > We are going around QOM based CPU introspecting interface for
> > years now and that's exactly what 2nd layer is, just another
> > implementation. I've just lost hope in this approach.
> > 
> > What I'm suggesting in this RFC is to forget controversial
> > QOM approach for now and use -device/device_add + QMP introspection,
> 
> You have a point about it looking controversial, but I would like
> to understand why exactly it is controversial. Discussions seem
> to get stuck every single time we try to do something useful with
> the QOM tree, and I don't undertsand why.

Yeah, I've noticed that too, and I don't know why either.

It's pretty frustrating, since on power we don't have the option of
sticking with the old cpu hotplug interface for now.  So I really have
no idea how to move things forwards towards a workable approach.

> > i.e. completely split interface from how boards internally implement
> > CPU hotplug.
> 
> A QOM-based interface may still split the interface from how
> boards internally implement CPU hotplug. They don't need to
> affect the device tree of the machine, we just need to create QOM
> objects or links at predictable paths, that implement certain
> interfaces.

-- 
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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