1. Is MPI still part of the solution ? George Bosilca Innovative Computing Laboratory Electrical Engineering and Computer Science Department University of Tennessee

2. Few notes about MPI MPI is not that easy: Simple MPI programs are easy but smart MPI programs are difficult MPI is not perfect, but it is as good as people could design it 10 years ago MPI Standard is not the root of all problems, one should look more at implementations MPI is not a fit-all solution. It enforce a flat programming model. Each communication has a cost. If your algorithm allow you to decrease the amount of exchanged data, then this new incarnation is more scalable. Portability !!! Why people expect MPI to ALWAYS deliver the best performance on a specific architecture ?

3. Is MPI ready for multi-core Depend on how we plan to use these multi / many cores: One process per node One process per core (*) Portability: For a long time MPI tried to hide the architectural details from the user. Internally we know, and we adapt. Is this still the right way to go ? How much should we expose to the user ?

4. Memory constraints The business card exchange problem What is the cost of MPI_COMM_WORLD on a Petascale machine ? Exascale ? MPI encourage users to create their own communicators … Each additional library you’re using has it’s own communicator(s)

5. Collective Communications The most optimized algorithm we have today are based on one strong assumption: all involved processes enter the collective simultaneously These algorithms try to optimize the network usage based on the supposition that during the collective MPI “own” the network. A more asynchronous approach will be required at scale (i.e. think overlap) Multi/Many cores systems require us to take the memory hierarchies in account Tuning the algorithms is the key …

6. What might be new on MPI 3.0 APPLICATION BINARY INTERFACE COLLECTIVE OPERATIONS FAULT TOLERANCE FORTRAN BINDINGS GENERALIZED REQUESTS MPI SUB-SETTING POINT-TO-POINT COMMUNICATIONS REMOTE MEMORY ACCESS http://meetings.mpi-forum.org/

7. What might be new on MPI 3.0 APPLICATION BINARY INTERFACE COLLECTIVE OPERATIONS FAULT TOLERANCE FORTRAN BINDINGS GENERALIZED REQUESTS MPI SUB-SETTING POINT-TO-POINT COMMUNICATIONS REMOTE MEMORY ACCESS http://meetings.mpi-forum.org/ The next MPI Forum will be held in Menlo Park, CA from June 30-July 2, 2008. Feel free to join us !!! The next MPI Forum will be held in Menlo Park, CA from June 30-July 2, 2008. Feel free to join us !!!

8. Another possible MPI based approach MPI as a communication library is a “must have”. Whatever the next programming paradigm will be, it has to include MPI (at least parts) Move toward a multi-level programming approach Allow thread to exchange data in between Point-to-point is possible today Collective is what we’re looking at

9. Another possible MPI based approach Based on the previous experiments we will investigate how MPI will behave if each thread became a fully features MPI entity. Allowing threads to have a global rank Change the meaning of collective communications: one process can be involved in the collective with several data Our interest: We get back the “ownership” of the network

10. AtomS: A MPI aware compiler Extract the maximal degree of parallelism from an MPI application Allow the user to continue writing the MPI applications on a step-by- step approach And then based on the compiler knowledge about the algorithms and the MPI knowledge about the data movement Re-write the algorithms to create a computation/communication pipeline overlap communications and computations