On Fri, 2019-02-08 at 14:14 +0100, Jiri Denemark wrote: > On Fri, Feb 08, 2019 at 11:03:34 -0200, Daniel Henrique Barboza wrote: > > Some devices creates empty (= cpu-less) NUMA nodes to host > > its memory. This results in topologies where the following > > sanity rule does not apply as is: > > > > nodes * sockets * cores * threads = total_cpus > > > > As a result, a call to 'virsh nodeinfo' will return the default > > value (1) to nodes, sockets and threads, while cores defaults > > to the total_cpus value. For example, in a Power9 host that has > > 160 total cpus, 4 cpu-less NUMA nodes, 2 populated NUMA nodes, > > 1 socket per populated node, 20 cores per socket and 4 threads > > per socket: > > > > $ virsh nodeinfo > > CPU model: ppc64le > > CPU(s): 160 > > CPU frequency: 3783 MHz > > CPU socket(s): 1 > > Core(s) per socket: 160 > > Thread(s) per core: 1 > > NUMA cell(s): 1 > > Memory size: 535981376 KiB > > > > This patch adjusts virHostCPUGetInfoPopulateLinux to count the > > cpu-less NUMA nodes and discard them in the sanity rule, changing > > it to: > > > > (nodes - empty_nodes) * sockets * cores * threads = total_cpus > > > > And with this new rule, virsh nodeinfo will return the > > appropriate info for those topologies, without changing the > > behavior for any other scenario it was previously working. > > > > This is the resulting output of nodeinfo after this patch in the > > same Power9 host mentioned above: > > > > $ virsh nodeinfo > > CPU model: ppc64le > > CPU(s): 160 > > CPU frequency: 3783 MHz > > CPU socket(s): 1 > > Core(s) per socket: 20 > > Thread(s) per core: 4 > > NUMA cell(s): 6 > > Memory size: 535981376 KiB > > This change would break backward compatibility as we have the following > public macro in libvirt-host.h: > > # define VIR_NODEINFO_MAXCPUS(nodeinfo) \ > ((nodeinfo).nodes*(nodeinfo).sockets*(nodeinfo).cores*(nodeinfo).threads) > > Anyway, the virNodeInfo structure is just not flexible enough to deal > with all possible topologies and users are advised to look at the host > capabilities XML to get a proper view of the host CPU topology. Correct, and it's even documented as such: https://libvirt.org/html/libvirt-libvirt-host.html#virNodeInfo So, as long as the number of CPUs is reported correctly (which it seems to be) and 'virsh capabilities' doesn't report incorrect information in the <topology> element, then there's nothing to be fixed - except for applications that still use virNodeInfo ;) -- Andrea Bolognani / Red Hat / Virtualization
