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Parallel Programming models I

Parallel Programming models I. Parallel Machines: an abstract introduction. Our main focus will be on three kinds of machines Bus-based shared memory machines Scalable shared memory machines Cache coherent Hardware support for remote memory access Distributed memory machines.

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Parallel Programming models I

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  1. Parallel Programming models I

  2. Parallel Machines: an abstract introduction • Our main focus will be on three kinds of machines • Bus-based shared memory machines • Scalable shared memory machines • Cache coherent • Hardware support for remote memory access • Distributed memory machines

  3. Bus based machines Mem0 Mem1 Memk PE0 PE1 PE N-1

  4. Bus based machines • Any processor can access any memory location • Read and write • Bus bandwidth is a limiting factor • Also, how do you deal with 2 processors changing the same data? • Locks (more on this later)

  5. Scalable shared memory m/cs PE0 PE0 PE0

  6. Scalable shared memory m/cs PE0 PE0 PE0 Interconnection Network with support for remote memory access Mem0 Mem0 Mem0

  7. Distributed memory m/cs PE0 PE0 PE0 Interconnection Network Mem0 Mem0 Mem0

  8. Writing parallel programs • Programming model • How should a programmer view the parallel machine? • Sequential programming: von Neumann model • Parallel programming models: • Shared memory (Shared address space) model • Message passing model • Shared Objects model

  9. Shared Address Space Model • All memory is accessible to all processes • Processes are mapped to processors, typically by a symmetric OS • Coordination among processes: • by sharing variables • Avoid “stepping on toes”: • using locks and barriers

  10. Matrix multiplication for (i=0; i<M; i++) for (j=0; j<N; j++) for (k=0; k<N; k++) C[I][j] += A[i][k]*B[k][j]; In a shared memory style, this program is trivial to parallelize Just have each processor deal with a different range of I (or J?) (or Both?)

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