Hello Youri,
When using openmpi 1.4.4 with --np 2 --bind-to-core --bycore” it reports the following:

[hostname:03339] [[17125,0],0] odls:default:fork binding child [[17125,1],0] to cpus 0001

[hostname:03339] [[17125,0],0] odls:default:fork binding child [[17125,1],1] to cpus 0002


Bitmask 0001 and 0002 mean CPUs with physical indexes 0 and 1 in OMPI 1.4. So that corresponds to the first core of each socket, and that matches what hwloc-ps says. Try "hwloc-ps -c" should show the same bitmask.

However, I agree that these are not adjacent cores, but I don't know enough of OMPI binding options to understand what it was supposed to do in your case.

Brice