On Tue, Oct 17, 2017 at 09:27:02AM +0200, Igor Mammedov wrote: > On Mon, 16 Oct 2017 17:36:36 +0100 > "Daniel P. Berrange" <berra...@redhat.com> wrote: > > > On Mon, Oct 16, 2017 at 06:22:50PM +0200, Igor Mammedov wrote: > > > Series allows to configure NUMA mapping at runtime using QMP/HMP > > > interface. For that to happen it introduces a new '-paused' CLI option > > > which allows to pause QEMU before machine_init() is run and > > > adds new set-numa-node HMP/QMP commands which in conjuction with > > > info hotpluggable-cpus/query-hotpluggable-cpus allow to configure > > > NUMA mapping for cpus. > > > > What's the problem we're seeking solve here compared to what we currently > > do for NUMA configuration ? > From RHBZ1382425 > " > Current -numa CLI interface is quite limited in terms that allow map > CPUs to NUMA nodes as it requires to provide cpu_index values which > are non obvious and depend on machine/arch. As result libvirt has to > assume/re-implement cpu_index allocation logic to provide valid > values for -numa cpus=... QEMU CLI option.
In broad terms, this problem applies to every device / object libvirt asks QEMU to create. For everything else libvirt is able to assign a "id" string, which is can then use to identify the thing later. The CPU stuff is different because libvirt isn't able to provide 'id' strings for each CPU - QEMU generates a psuedo-id internally which libvirt has to infer. The latter is the same problem we had with devices before '-device' was introduced allowing 'id' naming. IMHO we should take the same approach with CPUs and start modelling the individual CPUs as something we can explicitly create with -object or -device. That way libvirt can assign names and does not have to care about CPU index values, and it all works just the same way as any other devices / object we create ie instead of: -smp 8,sockets=4,cores=2,threads=1 -numa node,nodeid=0,cpus=0-3 -numa node,nodeid=1,cpus=4-7 we could do: -object numa-node,id=numa0 -object numa-node,id=numa1 -object cpu,id=cpu0,node=numa0,socket=0,core=0,thread=0 -object cpu,id=cpu1,node=numa0,socket=0,core=1,thread=0 -object cpu,id=cpu2,node=numa0,socket=1,core=0,thread=0 -object cpu,id=cpu3,node=numa0,socket=1,core=1,thread=0 -object cpu,id=cpu4,node=numa1,socket=2,core=0,thread=0 -object cpu,id=cpu5,node=numa1,socket=2,core=1,thread=0 -object cpu,id=cpu6,node=numa1,socket=3,core=0,thread=0 -object cpu,id=cpu7,node=numa1,socket=3,core=1,thread=0 (perhaps -device instead of -object above, but that's a minor detail) Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
