Collective Communication in Wormhole-Routed Massively Parallel Computers

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The supercomputing industry is now dominated by parallel architectures. In many such systems, memory is physically distributed among processors in order to achieve better scalability, requiring nodes to communicate through a network. In order to reduce communication latency, many systems have the wormhole-routing switching strategy, in which messages are pipelined through and a single destination, or collective. Communication operations may be either point-to-point, which involves a single source and a single destination, or collective, in which more than two processes participate. Collective communication operations are particularly important in scientific computing, where large data arrays are distributed over the local memories of the nodes, but are manipulated through single operations. This research project addresses the design of collective communication operations for wormhole-routed networks. The research is intended to explore architectural and algorithmic alternatives in the design of communications subsystems for next generation wormhole-routed networks. The project can be divided approximately into four subareas. First, both models will be used to develop new algorithms for collective operations in addition to those already under investigation. Target platforms will include both direct networks, as well as wormhole-routed switch-based interconnects. Second, the resulting algorithms will be applied in order to support higher-level parallel programming constructs, such as virtual process topologies, parallel I/O operations and distributed shared memory. Third, the resulting communication services will be used to improve the performance of parallel applications, in particular parallel numerical algorithms. Finally, the use of the new models will be investigated in wormhole-routed systems that serve purposes other than parallel computing, such as high speed local area networks. The methods used will be analysis, simulation, and experimental studies on commercial wormhole-routed systems. The significance of this research is that it will provide new solutions to the communication needs of parallel applications. Besides providing a better understanding of the issues and problems that must be addressed in design and use of collective operations in wormhole-routing systems, this project will produce tangible results in the form of new protocols, prototype implementations of new algorithms, and new applications software, all of which will be made publicly available for use by other researchers.