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Non-Collective Communicator Creation

Non-Collective Communicator Creation. Tickets #286 and #305 int MPI_Comm_create_group(MPI_Comm comm , MPI_Group group, int tag, MPI_Comm * newcomm ). Non-Collective Communicator Creation in MPI . Dinan, et al., Euro MPI ‘11. Non-Collective Communicator Creation.

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Non-Collective Communicator Creation

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  1. Non-Collective Communicator Creation Tickets #286 and #305 intMPI_Comm_create_group(MPI_Commcomm, MPI_Group group, int tag, MPI_Comm *newcomm) Non-Collective Communicator Creation in MPI. Dinan, et al., Euro MPI ‘11.

  2. Non-Collective Communicator Creation • Current: Collective on parent • Proposed: Create communicatorcollectively only on new members • Avoid coarse-grain synchronization • Load balancing: Reassign processes fromidle groups to active groups • Reduce overhead • Multi-level parallelism, create small communicators • Recovery from failures • Not all ranks in parent can participate • Compatibility with Global Arrays • Past: collectives using MPI Send/Recv 

  3. Evaluation: Microbenchmark O(log2 g) O(logp)

  4. Case Study: Markov Chain Monte Carlo • Dynamical nucleation theoryMonte Carlo (DNTMC) • Markov chain Monte Carlo • Part of NWChem • Multiple levels of parallelism • Multi-node “Walker” groups • Walker: N random samples • Load imbalance across groups • Regroup idle processes into active group • 37% decrease in total application execution time • Load Balancing of Dynamical Nucleation Theory Monte Carlo Simulations Through Resource Sharing Barriers [IPDPS ‘12] T L Winduset al 2008 J. Phys.: Conf. Ser.125 012017

  5. Update: Tagged Collectives Tag Space • Define two tag spaces: • Point-to-point tag space • Tagged collectives tag space • Spaces share the same semantics • MPI_TAG_UB • MPI_TAG_ANY • … • Tags match only within the same space • Ticket #305: Extend MPI_Intercomm_create(…) to use TCTS • Backward compatible, much easier to use

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