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