[libvirt] [PATCH v1 1/1] virhostcpu.c: consider empty NUMA nodes in topology validation

[Jiri Denemark]

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.

Jirka