Optimized Pipelined Parallel Merge Sort on the Cell BE
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- Keller J., Kessler C.W. (2009) Optimized Pipelined Parallel Merge Sort on the Cell BE. In: César E. et al. (eds) Euro-Par 2008 Workshops - Parallel Processing. Euro-Par 2008. Lecture Notes in Computer Science, vol 5415. Springer, Berlin, Heidelberg
Chip multiprocessors designed for streaming applications such as Cell BE offer impressive peak performance but suffer from limited bandwidth to off-chip main memory. As the number of cores is expected to rise further, this bottleneck will become more critical in the coming years. Hence, memory-efficient algorithms are required. As a case study, we investigate parallel sorting on Cell BE as a problem of great importance and as a challenge where the ratio between computation and memory transfer is very low. Our previous work led to a parallel mergesort that reduces memory bandwidth requirements by pipelining between SPEs, but the allocation of SPEs was rather ad-hoc. In our present work, we investigate mappings of merger nodes to SPEs. The mappings are designed to provide optimal trade-offs between load balancing, buffer memory consumption, and communication load on the on-chip bus. We solve this multi-objective optimization problem by deriving an integer linear programming formulation and compute Pareto-optimal solutions for the mapping of merge trees with up to 127 merger nodes. For mapping larger trees, we give a fast divide-and-conquer based approximation algorithm. We evaluate the sorting algorithm resulting from our mappings by a discrete event simulation.
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