On Wed, Oct 18, 2017 at 04:44:35PM +0200, Igor Mammedov wrote: > On Wed, 18 Oct 2017 10:59:11 -0200 > Eduardo Habkost <ehabk...@redhat.com> wrote: > > > On Tue, Oct 17, 2017 at 06:18:59PM +0200, Igor Mammedov wrote: > > > On Tue, 17 Oct 2017 17:09:26 +0100 > > > "Daniel P. Berrange" <berra...@redhat.com> wrote: > > > > > > > On Tue, Oct 17, 2017 at 06:06:35PM +0200, Igor Mammedov wrote: > > > > > On Tue, 17 Oct 2017 16:07:59 +0100 > > > > > "Daniel P. Berrange" <berra...@redhat.com> wrote: > > > > > > > > > > > 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 > > > > > the follow up question would be where do "socket=3,core=1,thread=0" > > > > > come from, currently these options are the function of > > > > > (-M foo -smp ...) and can be queried vi query-hotpluggble-cpus at > > > > > runtime after qemu parses -M and -smp options. > > > > > > > > Also, note that in the case of NUMA, having identifiers for CPU > > objects themselves won't be enough. NUMA settings need > > identifiers for CPU slots (even if they are still empty), and > > those slots are provided by the machine, not created by the user. > > > > > > > > The sockets/cores/threads topology of CPUs is something that comes from > > > > the libvirt guest XML config > > > in this case things for libvirt to implement would be to know following > > > details: > > > 1: which machine/machine version support which set of attributes > > > 2: valid values for these properties depending on machine/machine > > > version/cpu type > > > > The big assumption in this series is that libvirt doesn't know in > > advance how the possible slots for CPUs will look like on each > > machine-type, and need to query them using > > query-hotpluggable-cpus. > yep, that's true and it started with introduction of 'device_add cpu' > where libvirt didn't new what to specify as options for new cpu, > hence query-hotpluggable-cpus were added to provide that information. > > > > But if this assumption was really true, it would be impossible > > for the user to even decide how the NUMA topology will look like, > > wouldn't it? > > > > Igor, are you able to give one example of how the user input > > (libvirt XML) for configuring NUMA CPU binding could look like if > > the user didn't know yet what the available sockets/cores/threads > > are? > not sure I parse question but looking at libvirt's domain docs > it mentions > <numa> > <cell id='0' cpus='0-3' memory='512000' unit='KiB'/> > <cell id='1' cpus='4-7' memory='512000' unit='KiB' memAccess='shared'/> > </numa> > > here libvirt assumes that there are cpus with cpu-index in range 0-7 > /and probably duplicates logic that calculates cpu-index/ > If libvirt would continue to duplicate logic we could skip on > implementing early runtime QMP in QEMU and also drop support for > query-hotpluggable-cpus as libvirt would be able to compute > properties/values on it's own.
>From the POV of the XML, these CPU numbers are *not* required to be the same as any QEMU CPU index. This is just saying that we've got a <vcpus>8</vcpu> element, and we want the first 4 CPUs in one node and the second 4 in the second node. If QEMU assigns CPU indexes 70-77 internally, that's not relevant to the XML POV, which uses 0-7 regardless. If there ever was such a disjoint representation of CPU indexes libvirt would have to remap whats in the XML to match whats in QEMU 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 :|
