IBM RS/6000 SP interconnection network topologies for large systems

While the interconnection network topology is one of the most important determinants of the performance of a parallel system, no single topology offers an ideal cost/performance trade-off for all classes of applications in parallel processing. The modular units used in the IBM RS/6000 SP topologies allow the construction of a large variety of topologies including 4-ary fat-tree networks. In our experience, however, cost and cost/performance ratio are often the primary concerns of customers. Therefore, while fat-tree topologies offer excellent performance, they are not always the most attractive choice for customers of large-scale parallel systems. This paper presents the lower-cost RS/6000 SP topologies for large systems designed with fewer switching elements than fat-tree networks, and describes some of the rationale behind the choices made.