On Fri, 8 Jul 2016 09:46:00 +0200 Peter Krempa <pkre...@redhat.com> wrote:
> On Fri, Jul 08, 2016 at 12:23:08 +1000, David Gibson wrote: > > On Thu, 7 Jul 2016 17:17:14 +0200 > > Peter Krempa <pkre...@redhat.com> wrote: > > > > > Add a helper that looks up the NUMA node for a given CPU and use it to > > > fill the node_id in the PPC and X86 impls of query-hotpluggable-cpus. > > > > > > IIUC how the query thing works this means that the node id issued by > > query-hotpluggable-cpus will be echoed back to device add by libvirt. > > It will be echoed back, but the problem is that it's configured > separately ... > > > I'm not sure we actually process that information in the core at > > present, so I don't know that that's right. > > > > We need to be clear on which direction information is flowing here. > > Does query-hotpluggable-cpus *define* the NUMA node allocation which is > > then passed to the core device which implements it. Or is the NUMA > > allocation defined elsewhere, and query-hotpluggable-cpus just reports > > it. > > Currently (in the pre-hotplug era) the NUMA topology is defined by > specifying a CPU numbers (see previous patch) on the commandline: > > -numa node=1,cpus=1-5,cpus=8,cpus=11... > > This is then reported to the guest. > > For a machine started with: > > -smp 5,maxcpus=8,sockets=2,cores=2,threads=2 > -numa node,nodeid=0,cpus=0,cpus=2,cpus=4,cpus=6,mem=500 > -numa node,nodeid=1,cpus=1,cpus=3,cpus=5,cpus=7,mem=500 > > you get the following topology that is not really possible with > hardware: > > # lscpu > Architecture: x86_64 > CPU op-mode(s): 32-bit, 64-bit > Byte Order: Little Endian > CPU(s): 5 > On-line CPU(s) list: 0-4 > Thread(s) per core: 1 > Core(s) per socket: 2 > Socket(s): 2 > NUMA node(s): 2 > Vendor ID: GenuineIntel > CPU family: 6 > Model: 6 > Model name: QEMU Virtual CPU version 2.5+ > Stepping: 3 > CPU MHz: 3504.318 > BogoMIPS: 7008.63 > Hypervisor vendor: KVM > Virtualization type: full > L1d cache: 32K > L1i cache: 32K > L2 cache: 4096K > NUMA node0 CPU(s): 0,2,4 > NUMA node1 CPU(s): 1,3 > > Note that the count of cpus per numa node does not need to be identical. > > As of the above 'query-hotpluggable-cpus' will need to report the data > that was configured above even if it doesn't make much sense in a real > world. > > I did not try the above on a PPC host and thus I'm not sure whether the > config above is allowed or not. It's not - although I'm not sure that we actually have something enforcing this. However, single cores *must* be in the same NUMA node - there's no way of reporting to the guest anything finer grained. > While for the hotplug cpus it would be possible to plug in the correct > one according to the requested use the queried data but with the current > approach it's impossible to set the initial vcpus differently. > > Peter > > Note: For libvirt it's a no-go to start a throwaway qemu process just to > query the information and thus it's desired to have a way to configure > all this without the need to query with a specific machine > type/topology. -- David Gibson <dgib...@redhat.com> Senior Software Engineer, Virtualization, Red Hat
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