Designing Deadlock-Free Turn-Restricted Routing Algorithms for Irregular Wormhole-routed Networks

Irregular networks connected by wormhole-routed switches are becoming increasingly popular for building networks of workstations for cost-effective parallel processing. A primary strategy to achieve deadlock-free routing in such networks is to first configure the links in a network into some specific directions, and then prohibit the turns that a message may traverse. A routing algorithm imposes fewer turn prohibitions will have a higher adaptively and thus a higher performance. In general, designing such a routing algorithm requires two basic components: (1) assigning link directions, and (2) determining a link-direction-based routing guideline. In this paper we examine various assignment rules and routing guidelines, from which different heuristics and criteria are proposed to construct a good routing algorithm. Their effectiveness in reducing turn prohibitions is investigated, and in most cases the minimum turn prohibitions can be achieved. For a connected network with N switches and M links, the complexity of finding the set of turn prohibitions using our proposed method is O(N × M).