Open MPI currently has very limited cartesian support -- it actually doesn't remap anything.
That being said, it is *very* easy to extend Open MPI's algorithms for cartesian partitioning. As you probably already know, Open MPI is all about its plugins -- finding and selecting a good set of plugins to use at run-time. Open MPI has many different types of plugins. One of these types of plugins performs the cartesian/graph mapping behind MPI_Cart_create (and friends) function(s). Would you have any interest in writing a partitioning algorithm for your needs within the context of a plugin? I'd be happy to walk you through the process; it's not too complicated (although we should probably move the discussion off to the Open MPI devel mailing list). On Jun 29, 2010, at 4:50 AM, Paul Hilscher wrote: > Dear OpenMPI list, > > I am using a MPI-parallelized simulation program, with a > domain-decomposition in 6-Dimensions. > In order to improve the scalability of my program I would like to know > according to what preferences > is MPI distributing the ranks when using MPI_Cart_create( reorder allowed). > > To explain my inquiry, imagine a 3-dimensional solver in X-Y-M and 4 > computing > nodes, each nodes consist of 4 Quad-Core CPUs (4(Node)x[ 4(CPUs) x 4(Cores))] > CPUs=64CPUs). > > Now I decompose all 3 dimensions by 4 (4x4x4 = 64) using MPI_Cart_create. > MPI has now several possibilities to map the problem e.g. X-M (locally) on a > node and > Y across the nodes, or Y-M (locally) and X across the nodes. > > Now my question is, how can I tell MPI that I want to distribute X-Y locally > while > M is distributed across nodes. The reason is that X-Y > communication ratio is much large (FFT) compared to M where we have only > 2 communications per time-step via an Allreduce. > An MPI implementation for the BlueGENE for example has an option > called mapfile where on can tell MPI how to map the dimensions onto > the Nodes. I did not found somethings similar for openmpi. > > Does anybody know how to achieve this mapping or could anybody > tell me where I could find some examples or tutorials ? > > Thank you very much for your help and best wishes > > Paul Hilscher > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users -- Jeff Squyres jsquy...@cisco.com For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
