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Subject: Re: [OMPI devel] RFC: Remove all other paffinity components
From: Barrett, Brian W (bwbarre_at_[hidden])
Date: 2010-05-17 18:36:58

I'd prefer we not commit something in opal/hwloc until we have a plan for supporting platforms without hwloc support (ie, Red Storm). I have no objection to your original RFC, but I had the impression at the time that you had a plan in place for non-hwloc supported platforms.


On May 17, 2010, at 5:26 PM, Jeff Squyres wrote:

> On May 15, 2010, at 4:39 PM, Ralph Castain wrote:
>> So, to ensure I understand, you are proposing that we completely eliminate the paffinity framework and commit to hwloc in its place?
> I think there's 2 issues here:
> - topology information
> - binding
> hwloc supports both. paffinity mainly supports binding; it also supports some minor socket/core mapping information stuff, but mainly as a means to support binding better. hwloc's topology information is far more complete than paffinity's.
> How about this? (and this is very half-baked)
> - commit hwloc to opal/hwloc; the entire tree can call it
> - it's still TBD how to compile this out (e.g., for embedded environments)
> - it *may* need something like #if OPAL_HAVE_HWLOC
> - split paffinity into two frameworks (because some OS's support one and not the other):
> - binding: just for getting and setting processor affinity
> - hwmap: just for mapping (board, socket, core, hwthread) <--> OS processor ID
> In this way, if hwloc ever dies, we can still have OS-specific plugins for these two things, and the #if OPAL_HAVE_HWLOC will be 0.
> hwloc provides a very rich API for traversing the topology information; I don't think the main OPAL/ORTE/OMPI code base necessarily needs all of that functionality for the general case -- i.e., the binding/hwmap information (e.g., just want to bind a process to (board 1, socket 3, core 2, hwthread 1)).
> Anything that needs the detailed hwloc information (e.g., tuning the sm btl based on cache sizes reported by hwloc) can use #if OPAL_HAVE_HWLOC to protect itself.
> --
> Jeff Squyres
> jsquyres_at_[hidden]
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  Brian W. Barrett
  Dept. 1423: Scalable System Software
  Sandia National Laboratories