Title: Adaptive Routing on the New Switch Chip for IBM SP Systems
Authors: Bulent Abali, Craig B. Stunkel, Jay Herring, Mohammed Banikazem, Dhabaleswar K. Panda, and Cevdet Aykanat
Status: Published in Journal of Parallel and Distributed Computing , vol. xx, no. x, pp. xx-xx, 2001.


The IBM RS/6000 SP is one of the most successful commercially available multicomputers. SP owes its success partially to the scalable, high bandwidth, low latency network. This paper describes the architecture of Switch3 switch chip, the recently developed third generation switching element which future IBM RS/6000 SP systems may be based on. Switch3 offers significant enhancements over the existing SP switch chips by incorporating advances in both VLSI technology and interconnection network research. One of the major new features of Switch2 is the incorporation of adaptive routing support into it. We describe the adaptive source routing architecture of the Switch2 chip which is a unique feature of this chip. The performance of the adaptive source routing and oblivious routing for a wide range of system characteristics and traffic patterns is evaluated. It is shown that adaptive source routing outperforms or performs comparably with oblivious routing. We propose two novel algorithms for generating adaptive routes specifications required for enabling the usage of adaptive source routing. The comparison between the cost of these two algorithms and the performance improvement obtained from using these algorithms are discussed. We also propose different output selection functions to be used in switching elements for implementing the adaptive routing. We evaluate and compare the performance of these selection functions and discover that the best selection functions for BMINs are not dependent on the traffic pattern, message size, or system size.

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