[Qemu-devel] qemu-ppc and NUMA topology

[Nishanth Aravamudan <nacc@linux.vnet.ibm.com>]

Hi Alexey,

I've been looking at hw/ppc/spapr.c::spapr_populate_memory() and ran
into a few questions:

1) The values from 1 to nb_numa_nodes are used as indices into the
node_mem array, but that is not populated, necessarily, linearly.
vl.c::add_node() uses the nodeid parameter as the index into node_mem,
if it is specified.

2) The node ID is based upon the index into the array, but it seems like
it should actually be based upon the nodeid specified, if any. That is,
we set the value at index 4 (which is statically the reference point in
'ibm,associativity-reference-points') of 'ibm,associativty' for each
'ibm,memory@....' node to the index we are currently at. But as
mentioned in 1) above that index isn't necessarily currently the nodeid
specified on the command-line.

What this all means, is that if I specify something like:

-numa node,nodeid=1,cpus=0-7,mem=2048 -numa
node,nodeid=5,cpus=8-15,mem=0 -numa node,nodeid=9,mem=2048

Linux sees:

numactl --hardware
available: 3 nodes (0-2)
node 0 cpus: 8 9 10 11 12 13 14 15
node 0 size: 0 MB
node 0 free: 0 MB
node 1 cpus: 0 1 2 3 4 5 6 7
node 1 size: 2024 MB
node 1 free: 1560 MB
node 2 cpus:
node 2 size: 0 MB
node 2 free: 0 MB

Maybe we don't really care about this, but I just noticed it when trying
to reproduce some really weird topologies from PowerVM.

Thanks,
Nish