On 2/8/19 3:07 PM, Andrea Bolognani wrote:
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 ;)
Fair enough. Guess it's better to leave this one alone then.
ps: is virNodeInfo somewhat deprecated for showing CPU topology then?
Thanks,
DHB
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