Analysis of topology-dependent MPI performance on Gemini networks

Current HPC systems utilize a variety of interconnection networks, with varying features and communication characteristics. MPI normalizes these interconnects with a common interface used by most HPC applications. However, network properties can have a significant impact on application performance. We explore the impact of the interconnect on application performance on the Blue Waters supercomputer. Blue Waters uses a three-dimensional, Cray Gemini torus network, which provides twice the Y-dimension bandwidth in the X and Z dimensions. Through several benchmarks, including a halo-exchange example, we demonstrate that application-level mapping to the network topology yields significant performance improvements.