《并行程序设计导论》 第三课.ppt

Efficiency Copyright ? 2010, Elsevier Inc. All rights Reserved Speedups of Parallel Matrix-Vector Multiplication Copyright ? 2010, Elsevier Inc. All rights Reserved Efficiencies of Parallel Matrix-Vector Multiplication Copyright ? 2010, Elsevier Inc. All rights Reserved Scalability A program is scalable if the problem size can be increased at a rate so that the efficiency doesn’t decrease as the number of processes increase. Copyright ? 2010, Elsevier Inc. All rights Reserved Scalability Programs that can maintain a constant efficiency without increasing the problem size are sometimes said to be strongly scalable. Programs that can maintain a constant efficiency if the problem size increases at the same rate as the number of processes are sometimes said to be weakly scalable. Copyright ? 2010, Elsevier Inc. All rights Reserved A PARALLEL SORTING ALGORITHM Copyright ? 2010, Elsevier Inc. All rights Reserved Sorting n keys and p = comm sz processes. n/p keys assigned to each process. No restrictions on which keys are assigned to which processes. When the algorithm terminates: The keys assigned to each process should be sorted in (say) increasing order. If 0 ≤ q r p, then each key assigned to process q should be less than or equal to every key assigned to process r. Copyright ? 2010, Elsevier Inc. All rights Reserved Serial bubble sort Copyright ? 2010, Elsevier Inc. All rights Reserved Odd-even transposition sort A sequence of phases. Even phases, compare swaps: Odd phases, compare swaps: Copyright ? 2010, Elsevier Inc. All rights Reserved Example Start: 5, 9, 4, 3 Even phase: compare-swap (5,9) and (4,3) getting the list 5, 9, 3, 4 Odd phase: compare-swap (9,3)getting the list 5, 3, 9, 4 Even phase: compare-swap (5,3) and (9,4) getting the list 3, 5, 4, 9 Odd phase: compare-swap (5,4)getting the list 3, 4, 5, 9 Copyright ? 2010, Elsevier Inc. All rights Reserved Serial odd-even transposition sort Copyright ? 2010, Elsevier Inc. All rights Reserve