Re: [PATCH 5/5] qemu: Prefer -numa cpu over -numa node,cpus=

On 10/20/21 1:18 PM, Peter Krempa wrote: > On Wed, Oct 20, 2021 at 13:07:59 +0200, Michal Prívozník wrote: >> On 10/6/21 3:32 PM, Igor Mammedov wrote: >>> On Thu, 30 Sep 2021 14:08:34 +0200 >>> Peter Krempa <pkrempa(a)redhat.com&gt; wrote: > > [...] > >> 2) In my experiments I try to mimic what libvirt does. Here's my cmd >> line: >> >> qemu-system-x86_64 \ >> -S \ >> -preconfig \ >> -cpu host \ >> -smp 120,sockets=2,dies=3,cores=4,threads=5 \ >> -object '{"qom-type":"memory-backend-memfd","id":"ram-node0","size":4294967296,"host-nodes":[0],"policy":"bind"}' \ >> -numa node,nodeid=0,memdev=ram-node0 \ >> -no-user-config \ >> -nodefaults \ >> -no-shutdown \ >> -qmp stdio >> >> and here is my QMP log: >> >> {"QMP": {"version": {"qemu": {"micro": 50, "minor": 1, "major": 6}, "package": "v6.1.0-1552-g362534a643"}, "capabilities": ["oob"]}} >> >> {"execute":"qmp_capabilities"} >> {"return": {}} >> >> {"execute":"query-hotpluggable-cpus"} >> {"return": [{"props": {"core-id": 3, "thread-id": 4, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, {"props": {"core-id": 3, "thread-id": 3, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, {"props": {"core-id": 3, "thread-id": 2, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, {"props": {"core-id": 3, "thread-id": 1, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, {"props": {"core-id": 3, "thread-id": 0, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, {"props": {"core-id": 2, "thread-id": 4, "die-id": 2, "socket-id": 1}, "vcpus-count": 1, "type": "host-x86_64-cpu"}, >> <snip/> >> {"props": {"core-id": 0, "thread-id": 0, "die-id": 0, "socket-id": 0}, "vcpus-count": 1, "type": "host-x86_64-cpu"}]} >> >> >> I can see that query-hotpluggable-cpus returns an array. Can I safely >> assume that vCPU ID == index in the array? I mean, if I did have -numa > > No, this assumption would be incorrect on the aforementioned PPC > platform where one entry in the returned array can describe multiple > cores. > > qemuDomainFilterHotplugVcpuEntities is the code that cross-references > the libvirt "index" with the data returned by query-hotpluggable cpus. > > The important bit is the 'vcpus-count' property. The code which deals > with hotplug is already fetching everything that's needed. Ah, I see. So my assumption would be correct if vcpus-count would be 1 for all entries. If it isn't then I need to account for how much

vcpus-count is in each entity. Fair enough. But qemuDomainFilterHotplugVcpuEntities() doesn't really do vCPU ID -> [socket, core, thread] translation, does it? But even if it did, I am still wondering what the purpose of this whole exercise is. QEMU won't be able to drop ID -> [socket, core, thread] mapping. The only thing it would be able to drop is a few lines of code handling command line. Am I missing something obvious?

Michal