Portable and scalable algorithms for irregular all-to-all communication

In this paper we develop portable and scalable algorithms for performing irregular all-to-all communication in High Performance Computing (HPC) systems. To minimize the communication latency, the algorithm reduces the total number of messages transmitted, reduces the variance of the lengths of these messages, and overlaps the communication with computation. The performance of the algorithm is characterized using a simple model of HPC systems. Our implementations are performed using the Message Passing Interface (MPI) standard and they can be ported to various HPC platforms. The performance of our algorithms is evaluated on CM5, T3D and SP2. The results show the effectiveness of the techniques as well as the interplay between the architectural features, the machine size, and the variance of message lengths. The experiences of our study can be applied in other HPC systems to optimize the performance of collective communication operations.