Dynamic memory usage in parallel simulation: a case study of a large-scale military logistics application

We report on a comparative study of the performance of shared and distributed memory parallel simulation algo rithms on a large-scale military logistics simulation, and describe the nature of the application and its parallelisa tion in some detail. We demonstrate that the patterns of communication in the simulation were such that a standard implementation of Breathing Time Buckets (BTB) was unable to achieve any speed-up. New variants of BTB were designed and implemented, and we were able to achieve a speed-up of 7.4 compared to a critical path limit of 16.9. The logistics simulation contained a number of complex data structures and its parallel implementation was highly memory-intensive. The resulting patterns of memory access significantly degraded the shared memory simulation performance relative to the equivalent distributed memory version. These results cast doubt on the effectiveness of the current generation of shared memory parallel computers in dealing with optimistic simulations of large, dynamic scenarios.