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Subject: [OMPI devel] RFC: hwloc object userdata
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-10-03 10:13:28


WHAT: allowing multiple entities in the OMPI code base to hang data off hwloc_obj->userdata

WHY: anticipating that more parts of the OMPI code base will be using the hwloc data

WHERE: hwloc base

WHEN: no real hurry; Ralph and I just identified the potential for this issue this morning. We're not aware of it being an actual problem (yet).

MORE DETAIL:

The rmaps base (in mpirun) is currently hanging its own data off various objects in the hwloc topology tree. However, it should be noted that the hwloc topology tree is a global data structure in each MPI processes; multiple upper-level entities in the ORTE and OMPI layers may want to hang their own userdata off hwloc objects.

Ralph and I figured that some functionality could be added to the hwloc base to hang a opal_pointer_array off each hwloc object; each array value will be a (void*). Then upper-level entities can reserve a slot in all the pointer arrays and store whatever they want in their (void*) slot.

For example, if the openib BTL wants to use the hwloc data and hang its own userdata off hwloc objects, it can call the hwloc base and reserve a slot. The hwloc base will say "Ok, you can have slot 7". Then the openib BTL can always use slot 7 in the opal_pointer_array off any hwloc object.

Does this sound reasonable?

-- 
Jeff Squyres
jsquyres_at_[hidden]
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