Re: [libvirt] [Qemu-devel] Exposing and calculating CPU APIC IDs (was Re: [RFC 1/3] target-i386: moving registers of vmstate from cpu_exec_init() to x86_cpu_realizefn())

On Tue, 2014-01-21 at 11:10 +0100, Andreas Färber wrote: > Am 21.01.2014 10:51, schrieb Chen Fan: > > On Tue, 2014-01-21 at 10:31 +0100, Igor Mammedov wrote: > >> On Tue, 21 Jan 2014 15:12:45 +0800 > >> Chen Fan <chen.fan.fnst(a)cn.fujitsu.com&gt; wrote: > >>> On Mon, 2014-01-20 at 13:29 +0100, Igor Mammedov wrote: > >>>> On Fri, 17 Jan 2014 17:13:55 -0200 > >>>> Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote: > >>>>> On Wed, Jan 15, 2014 at 03:37:04PM +0100, Igor Mammedov wrote: > >>>>>> I recall there were objections to it since APIC ID contains topology > >>>>>> information and it's not trivial for user to get it right. > >>>>>> The last idea that was discussed to fix it was not expose APIC ID to > >>>>>> user but rather introduce QOM hierarchy like: > >>>>>> /machine/node/N/socket/X/core/Y/thread/Z > >>>>>> and use it in user interface as a means to specify an arbitrary CPU > >>>>>> and let QEMU calculate APIC ID based on this path. > >>>>>> > >>>>>> But nobody took on implementing it yet. > >>>>> > >>>>> We're taking so long to get a decent interface implemented, that part of > >>>>> me is considering exposing the APIC ID directly like suggested before, > >>>>> and requiring libvirt to calculate topology-aware APIC IDs[1] to > >>>>> properly implement CPU hotplug (and possibly for other tasks). > >>>> If you are speaking about > >>>> 'qemu will core dump with "-smp 254, sockets=2, cores=3, threads=2"' > >>>> http://patchwork.ozlabs.org/patch/301272/ > >>>> bug then it's limitation of ACPI implementation, > >>>> I'm going to refactor it to use full APIC ids instead of using bitmap, > >>>> so that we won't ever run into issue regardless of cpu supported CPU count. > >>>> > >>>>> > >>>>> Another part of me is hoping that the libvirt developers ask us to > >>>>> please not do that, so I can use it as argument against exposing the > >>>>> APIC IDs directly the next time we discuss this. :) > >>>> > >>>> why not try your /machine/node/N/socket/X/core/Y/thread/Z idea first. > >>>> It will benefit not only cpu hotplug but also '-numa' and topology > >>>> description in general. > >>>> > >>> have there been any plan/model of the idea? Need to add a new option to > >>> qemu command? > >> I suppose we can start with internal default implementation first. > >> > >> one way could be > >> 1. let machine prebuild empty QOM tree /machine/node/N/socket/X/core/Y/thread/Z > >> 2. add node, socket, core, thread properties to CPU and link CPU into respective > >> link created by #1 > >> > > Thanks, I hope I can take some time to make some patches to implement > > it. > > Please give us a few hours to reply. :) > > /machine/node seems too broad a term to me. > You can't prebuild the full tree, you can only prepare the nodes. > core[Y]/thread[Z] was previously discussed as syntax. > > The important part to decide on will be what is going to be child<> and > what link<>. Has anyone played with the Intel Quark platform for > instance? (Galileo board or upcoming Edison card) On a regular > mainboard, we would have socket[X] as a link<x86_64-cpu>, which might > point to a child<cpu> /machine/memory-node[W]/cpu[X]. But if we do so we > can't reassign it to another memory node - acceptable? With Quark (or > Qseven modules etc.) there would be a container object rather than the > /machine itself that has a child<i386-cpu> instead of a link<i386-cpu>. > I guess the memory nodes could still be on the /machine though. > The other point of discussion between Anthony and me was whether core[Y] > should be a link<> or child<>, same for thread. I believe a child<> is > better as it enforces that unrealizing the CPU will unrealize all its > cores and all its threads in the future. > > More issues may pop up when thinking about it longer than a few minutes. > But yes, we need to start investigating this, and so far I had other > priorities like getting the CPUState mess I created cleaned up. Hi, Igor, Andreas, In addition, I want to know what way user could use to specify an arbitrary CPU if using /machine/node/N/socket/X/core/Y/thread/Z idea? -device qemu64,socket=X,core=Y,thread=Z? or add a new optional command line?

Thanks, Chen > > Regards, > Andreas >