LFTI: A New Performance Metric for Assessing Interconnect Designs for Extreme-Scale HPC Systems

Traditionally, interconnect performance is either characterized by simple topological parameters such as bisection bandwidth or studied through simulation that gives detailed performance information for the scenarios simulated. Neither of these approaches provides a good performance overview for extreme-scale interconnects. The topological parameters are not directly related to application level communication performance while the simulation complexity limits the number of scenarios that can be investigated. In this work, we propose a new performance metric, called LANL-FSU Throughput Indices (LFTI), for characterizing the throughput performance of interconnect designs. LFTI combines the simplicity of topological parameters and the accuracy of simulation: like topological parameters, LFTI can be derived from interconnect specification, at the same time, it directly reflects the application level communication performance. Moreover, in cases when the theoretical throughput for each communication pattern can be modeled efficiently for an interconnect, LFTI for the interconnect can be computed efficiently. These features potentially allow LFTI to be used for rapid and comprehensive evaluation and comparison of extreme-scale interconnect designs. We demonstrate the effectiveness of LFTI by using it to evaluate and explore the design space of a number of large-scale interconnect designs.