›› 2013, Vol. 28 ›› Issue (4): 657-670.doi: 10.1007/s11390-013-1366-9

Special Issue: Computer Architecture and Systems

• Architecture and VLSI Design • Previous Articles     Next Articles

Optimizing Parallel Sn Sweeps on Unstructured Grids for Multi-Core Clusters

Jie Yan1,2 (闫洁), Student Member, IEEE, Guang-Ming Tan1 (谭光明), Member, CCF, ACM, IEEE and Ning-Hui Sun1 (孙凝晖), Fellow, CCF, Member, ACM, IEEE   

  1. 1. State Key Laboratory of Computer Architecture, Institute of Computing Technology, Chinese Academy of Sciences Beijing 100190, China;
    2. University of Chinese Academy of Sciences, Beijing 100049, China
  • Received:2012-05-10 Revised:2013-02-07 Online:2013-07-05 Published:2013-07-05
  • Supported by:

    This work is supported by the National Natural Science Foundation of China under Grant Nos. 60925009, 61003062, 61033009, 61272134, and the National Basic 973 Program of China under Grant Nos. 2011CB302502 and 2012CB316502.

In particle transport simulations, radiation effects are often described by the discrete ordinates (Sn) form of Boltzmann equation. In each ordinate direction, the solution is computed by sweeping the radiation flux across the grid. Parallel Sn sweep on an unstructured grid can be explicitly modeled as topological traversal through an equivalent directed acyclic graph (DAG), which is a data-driven algorithm. Its traditional design using MPI model results in irregular communication of massive short messages which cannot be efficiently handled by MPI runtime. Meanwhile, in high-end HPC cluster systems, multicore has become the standard processor configuration of a single node. The traditional data-driven algorithm of Sn sweeps has not exploited potential advantages of multi-threading of multicore on shared memory. These advantages, however, as we shall demonstrate, could provide an elegant solution resolving problems in the previous MPI-only design. In this paper, we give a new design of data-driven parallel Sn sweeps using hybrid MPI and Pthread programming, namely Sweep-H, to exploit hierarchical parallelism of processes and threads. With special multi-threading techniques and vertex schedule policy, Sweep-H gets more efficient communication and better load balance. We further present an analytical performance model for Sweep-H to reveal why and when it is advantageous over former MPI counterpart. On a 64-node multicore cluster system with 12 cores per node, 768 cores in total, Sweep-H achieves nearly linear scalability for moderate problem sizes, and better absolute performance than the previous MPI algorithm on more than 16 nodes (by up to two times speedup on 64 nodes).

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