Load Balancing and Performance of a Gridless Particle Simulation on MIMD, SIMD, and Vector Supercomputers

S. J. Plimpton, I. Shokair, J. Wagner, in Proc of 5th SIAM Conference on Parallel Processing for Scientific Computing, Houston, TX, March 1991, p 507- 512.

Our charged particle simulation models a relativistic electron beam for which the field solution is local and thus requires no grid. We have implemented the simulation on a CRAY and on two parallel machines, a nCUBE 2 and Connection Machine. We present implementation details and contrast the approaches necessary for the three architectures. On the parallel machines a dynamic load- balancing problem arises because the beam grows uniformly in one dimension from a few hundred to hundreds of thousands of particles as the simulation progresses. We discuss a folded Gray-code mapping of the processors to the length scale of the simulation that expands (or shrinks) as the beam changes length so as to minimize inter-processor communication. This improves the efficiency of the nCUBE version of the simulation which runs at 10x the speed of the vectorized CRAY version.

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