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Non-Collective Communicator Creation

Non-Collective Communicator Creation. Ticket #286 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 Ticket #286 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 • Currently: Collective operation • Non-Collective: Create communicatorcollectively only on new members • Avoid bulk synchronization • Load balancing: Reassign processes fromidle groups to active groups • Overhead reduction • Multi-level parallelism, small communicators • Recovery from failures • Not all ranks in parent can participate • Compatibility with Global Arrays • Past: collectives using MPI Send/Recv 

  3. Non-Collective Communicator Creation Algorithm 0 1 2 3 4 5 6 7 MPI_COMM_SELF (intracommunicator) MPI_Intercomm_create (intercommunicator) MPI_Intercomm_merge 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 ✓ 0 1 2 3 4 5 6 7

  4. Non-Collective Algorithm in Detail • R Translate group ranks toordered list of ranks onparent communicator Calculate my group ID Left group Right group

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

  6. Case Study: Markov Chain Monte Carlo • Dynamical nucleation theoryMonte Carlo (DNTMC) • Part of NWChem • Markov chain Monte Carlo • Multiple levels of parallelism • Multi-node “Walker” groups • Walker: N random samples • Load imbalance • Sample computation (energy calculation) is irregular, can be rejected • Regroup idle processes into active group • Preliminary results: 30% decrease in total application execution time T L Winduset al 2008 J. Phys.: Conf. Ser.125 012017

  7. Santorini straw vote to proceed with a formal reading:Yes ( 16 ), No ( 0 ), Abstain ( 1 )

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