Distribute n items over the topology under root.
Array cpuset will be filled with n cpusets distributed linearly over the topology under root .
This is typically useful when an application wants to distribute n threads over a machine, giving each of them as much private cache as possible and keeping them locally in number order.
The caller may typicall want to additionally call hwloc_cpuset_singlify() before binding a thread, so that it doesn't move at all.