Contention-free communication scheduling for array redistribution

Abstract

Array redistribution is required often in programs on distributed memory parallel computers. It is essential to use efficient algorithms for redistribution, otherwise the performance of the programs may degrade considerably. The redistribution overheads consist of two parts: index computation and interprocessor communication. If there is no communication scheduling in a redistribution algorithm, the communication contention may occur, which increases the communication waiting time. In order to solve this problem, we propose a technique to schedule the communication so that it becomes contention-free. Our approach initially generates a communication table to represent the communication relations among sending nodes and receiving nodes. According to the communication table, we then generate another table named communication scheduling table. Each column of the communication scheduling table is a permutation of receiving node numbers in each communication step. Thus the communications in our redistribution algorithm are contention-free. Our approach can deal with multi-dimensional shape changing redistribution.