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Communication Libraries for Parallel-Programming-Model Runtime Systems

Communication Libraries for Parallel-Programming-Model Runtime Systems. Andy Stone CS653. AndyStone -- CS653 Mini Research Exam Presentation , November 16, 2010 Slide 1. What I'll Talk About. Three communication libraries. Communication Operations.

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Communication Libraries for Parallel-Programming-Model Runtime Systems

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  1. Communication Libraries for Parallel-Programming-Model Runtime Systems Andy Stone CS653 AndyStone -- CS653 Mini Research Exam Presentation , November 16, 2010 Slide 1

  2. What I'll Talk About Three communication libraries Communication Operations How they've been tailored for a machine AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 2

  3. Context UEs (task/processes) need to communicate Why? Synchronize Computation Pass Data In a programming model communication can be implicit or explicit Example: Set array A on process 1 to array B on process 2 MPI: Explicit Co-Array Fortran: Implicit if(id == 1) { MPI_Recv(A, n, MPI_DOUBLE, 2, 0, MPI_COMM_WORLD); } else if(id ==2) { MPI_Send(B, n, MPI_DOUBLE, 1, 0, MPI_COMM_WORLD); } if(this_image() == 1) then A=B[2] end if AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 3

  4. Models and Communication Libraries Co-Array Fortran GlobalArrays CHAPEL AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 4

  5. Communication Operations Classification of communication operations: Blocking versus non-blocking Two-sided versus one-sided 2-sided: send, receive 1-sided: put, get, accumulate What ARMCI/GASNET has that MPI doesn't: - Stronger focus on 1-sided communication - Active Messages (RPC mechanism) - I/O vector and strided messages - ARMCI: Sum-and-scale in one accumulate operation AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 5

  6. Implementation Optimizations AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 6

  7. Implementation Optimizations J. Nieplocha and B. Carpenter. Armci: A portable remote memory copy library for distributed array libraries and compiler run-time systems. In Parallel and Distributed Processing, volume 1586 of Lecture Notes in Computer Science, pages 533{546. Springer Berlin / Heidelberg, 1999. Compare MPICH against IBM Experimentally determine the behavior of ISEND/IRECV Suggest optimization: Add in wait or test commands Show 27% reduction in communication time for SAMR example AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 7

  8. Implementation Optimizations D. Bonachea, P. H. Hargrove, M. Welcome, and K. Yelick. Porting gasnet to portals: Partitioned global address space (pgas) language support for the crayXT. In Cray Users Group, 2009. Modifying GASNet to use Cray XT's native communication library: Portals AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 8

  9. Implementation Optimizations J. Nieplocha and B. Carpenter. Armci: A portable remote memory copy library for distributed array libraries and compiler run-time systems. In Parallel and Distributed Processing, volume 1586 of Lecture Notes in Computer Science, pages 533{546. Springer Berlin / Heidelberg, 1999. Accumulate is implemented differently on different machines IBM SP: Owner-computes Cray T3E: Source-computes AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 9

  10. Conclusions Libraries very similar in terms of one-sided communication and synchronization operations they include. GASNET/ARMCI Used by programming model implementors Differences: GASNET/ARMCI: I/O Vector, Strided ARMCI: Scale-and-sum accumulate operation Performance of library implementation dependent, implementations are often tailored to work well with a specific machine. AndyStone -- CS653 Paper Review Presentation , Sept 21, 2010 Slide 10

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