Both bitmaps show all 24 cores, so hwloc is able to read sysfs and
determine the existence of 2 sockets with 12 nodes each, and where the
12 nodes are numbered 0-5 twice according to which bank of cache they
are tied to. Which version of libvirt is this tested on where libvirt
was only reporting 12 cores, because I thought we already patched that
with commit 80533ca in 0.10.0. That is, I think proc1.png should result in:

$ virsh nodeinfo
CPU model: x86_64
CPU(s): 24
CPU frequency: 2200 MHz

CPU socket(s): 2
Core(s) per socket: 12

Thread(s) per core: 1
NUMA cell(s): 1
Memory size: 8047272 KiB

(Just for clarity, I am the original reporter, sorry I couldn't answer earlier, I subscribed to the list too late and didn't want to break the thread)

On the host with 1 NUMA cell, with libvrit 0.10.2 I get:

[root@host29 ~]# virsh nodeinfo

CPU model: x86_64

CPU(s): 24

CPU frequency: 2200 MHz

CPU socket(s): 2

Core(s) per socket: 6

Thread(s) per core: 1

NUMA cell(s): 1

Memory size: 131971548 KiB

Furthermore, to answer the question at the bottom of your email, http://birzan.org/capabilities1.txt has this info.

and proc4.png would _ideally_ result in:

$ virsh nodeinfo
CPU model: x86_64
CPU(s): 24
CPU frequency: 2200 MHz

CPU socket(s): 2
Core(s) per socket: 12
Thread(s) per core: 1
NUMA cell(s): 4
Memory size: 8047272 KiB

[root@host34 ~]# virsh nodeinfo

CPU model: x86_64

CPU(s): 24

CPU frequency: 2200 MHz

CPU socket(s): 2

Core(s) per socket: 6

Thread(s) per core: 1

NUMA cell(s): 1

Memory size: 131971020 kB

And http://birzan.org/capabilities4.txt

This is on 0.9.11.5, on 0.10.2:

[root@host34 libvirt]# virsh nodeinfo

CPU model: x86_64

CPU(s): 24

CPU frequency: 2200 MHz

CPU socket(s): 1

Core(s) per socket: 6

Thread(s) per core: 1

NUMA cell(s): 4

Memory size: 131971020 KiB

and http://birzan.org/capabilities4-newlibvirt.txt

This has made the problem even worse, as we now can only use 6 cores out of 24 by default (libvirt pins qemus to the CPUs is sees available, so we have to manually taskset them after starting).

I think the CPU _is_ reporting the complete NUMA topology through sysfs,
but that we are probably consolidating information from the wrong files
and therefore getting confused.

The sysfs is tarred up in http://birzan.org/sysdevicessystem.tar.gz for host29 (the one with 1 numa cell in capabilities) and http://birzan.org/sysdevicessystem-34.tar.gz

Also, what does the 'virsh capabilities' report for the <topology>
section? Whereas 'virsh nodeinfo' is constrained by back-compat to give
a lame answer for number of NUMA cells, at least 'virsh capabilities'
should be showing a reasonable representation of the machine's topology.

I answered this above. If you need any more info, feel free to ask.