Re: [Qemu-devel] [RFC 0/5] Allow object-add on X86CPU subclasses, for CPU model probing

[Andreas Färber]

Am 15.05.2014 15:07, schrieb Eduardo Habkost:
> On Thu, May 15, 2014 at 02:35:01PM +0200, Igor Mammedov wrote:
>> On Tue, 06 May 2014 22:29:24 +0200
>> Andreas Färber <address@hidden> wrote:
>>
>>> Am 06.05.2014 22:19, schrieb Eduardo Habkost:
>>>> On Tue, May 06, 2014 at 10:01:11PM +0200, Igor Mammedov wrote:
>>>>> On Tue, 6 May 2014 11:42:56 -0300
>>>>> Eduardo Habkost <address@hidden> wrote:
>>>>>> On Tue, May 06, 2014 at 09:22:38AM +0200, Igor Mammedov wrote:
>>>>>>> On Fri, 2 May 2014 11:43:05 -0300
>>>>>>> Eduardo Habkost <address@hidden> wrote:
>>>>>>>> On Fri, May 02, 2014 at 03:45:03PM +0200, Igor Mammedov wrote:
>>>>>>>>> On Wed, 30 Apr 2014 17:29:28 -0300
>>>>>>>>> Eduardo Habkost <address@hidden> wrote:
>>>>>>>>>> This series allows management code to use object-add on X86CPU 
>>>>>>>>>> subclasses, so it
>>>>>>>>> Is there any reason why "device-add" couldn't be used?
>>>>>>>> It needs to work with "-machine none", device_add requires a bus to
>>>>>>>> exist, and there is no icc-bus on machine_none.
>>>>>>> The thing is that CPUID is a function of machine so using
>>>>>>> "-machine none" will provide only approximately accurate data.
>>>>>>> I'm not sure that retrieved possibly not accurate data are useful
>>>>>>> for libvirt.
>>>>>> "-cpu host" doesn't depend on machine, and is the most important thing
>>>>>> right now (because libvirt's checks for host QEMU/kernel/CPU
>>>>>> capabilities is completely broken).
>>>>> true, but device-add/-cpu host could be used right now to get the
>>>>> same CPUID data wile using any machine type or default one without
>>>>> any of this patches.
>>>>
>>>> device_add can't be used with "-machine none".
>>>
>>> I see no reason why we couldn't *make* CPUs work on -machine none. The
>>> ICC bus and bridge were a hack to make APIC(?) hot-add work in face of
>>> SysBus; if that prohibits other valid uses now, then evaluating Igor's
>>> memory work for CPU might be an option.
>> Yep, if CPU is hot-plugged as bus-less device.
>> There is a little concern of APIC device if we go that direction since
>> in addition to hotpluggable BUS, BUS provides address-space for APIC MMIO.
>> With that resolved, x86-cpu shouldn't depend on any bus and if there isn't
>> any current user that uses QOM path to CPU for introspecting (Eduardo's
>> ABI concern), then it could be done in time for 2.1.
> 
> Maybe there are no users of the current QOM path, but we do need a
> stable path to allow management to locate the CPU objects. Do we have
> one, already?

No, we don't. That question is intertwined with topology modeling. :/

Andreas

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