Re: [Qemu-devel] [PATCH 1/7] Introduce a new bus "ICC" to connect APIC

[Igor Mammedov]

On 02/16/2012 01:42 PM, Anthony Liguori wrote:
> On 02/16/2012 05:25 AM, Jan Kiszka wrote:
> > On 2012-02-16 00:16, Igor Mammedov wrote:
> > > Introduce a new structure CPUS as the controller of ICC (INTERRUPT
> > > CONTROLLER COMMUNICATIONS), and new bus "ICC" to hold APIC,instead
> > > of sysbus. So we can support APIC hot-plug feature.
> > >
> > > This is repost of original patch for qemu-kvm rebased on current qemu:
> > > http://lists.nongnu.org/archive/html/qemu-devel/2011-11/msg01478.html
> > > All credits to Liu Ping Fan for writing it.
> > >
> > > V2 changes:
> > > - cpusockets_init: cpu_sockets is not yet initialized, use cpus that
> > > we got as input param instead for qbus_create, this makes cpus
> > > apics visible in "info qtree" monitor command
> > > - fix format error spotted by Jan and missed by checkpatch
> > > - cpu_has_apic_feature: return bool instead of int
> >
> > This patch surely no longer applies. And the ICC requires QOM conversion.
>
> Also, post-QOM, I don't think having an ICC bus makes a whole lot of sense.
>
> The LAPIC can be made a child of the CPU device with a bidirectional link.
>
> I would simply create a fixed set of CPU links<> hung off of /devices somewhere 
> and use that as the hotplug mechanism. This matches well the way we
> model this to the guest (we expose a fixed number of pluggable sockets).

I've just QOM-ified it, but in light of what you just said it may be ignored.
ICC bus was used on pre Pentium 4 smp systems. And whole thing with introducing
it was to provide hot-plugable bus for cpus, since hot-plug on sysbus is 
disabled
and people argued that sysbus shouldn't be hot-plugable. However it depends on
what we choose to model, we can use pre P4 ICC bus for inter-apic/ioapic 
communications
or use P4 model allowing hot-plug on sysbus and use it for inter-apic/ioapic
communications if needed.

So I'd rather drop ICC patch and try your approach with CPU links<>, I see no
point in introducing new bus providing we have an alternative model and existing
bus for the task.

> Regards,
>
> Anthony Liguori
>
> > Jan

--
Thanks,
 Igor