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

On Thu, May 15, 2014 at 02:35:01PM +0200, Igor Mammedov wrote: > On Tue, 06 May 2014 22:29:24 +0200 > Andreas Färber <afaerber(a)suse.de&gt; 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 <ehabkost(a)redhat.com&gt; 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 <ehabkost(a)redhat.com&gt; 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 <ehabkost(a)redhat.com&gt; 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?