Adaptive routing can improve network performance and fault-tolerance by providing multiple routing paths. However, the implementation complexity of adaptive routing can be significant, discouraging its use in commercial massively parallel systems. In this paper we introduce Hierarchical Adaptive Routing (HAR), a new adaptive routing framework which provides a unified framework for simple and high performance fully adaptive deadlock-free wormhole routing. HAR divides the physical network into several levels of virtual networks. There is one connection channel between two adjacent virtual networks that allows blocked packets in the higher level to move to the lower level. Different routing algorithms can be used in each virtual network; and the overall network is deadlock-free provided the rotating algorithm in the lowest level virtual network is deadlock-free. However, the routing algorithm in any other virtual network can be fully adaptive, even non-minimal, to increase performance. HAR has three advantages: fully adaptive deadlock-free routing in any non-wrapped and wrapped k-ary n-cube network with 2 and 3 virtual channels respectively, relatively small crossbars, and applicability to a wide variety of network topologies. Detailed implementation and simulation studies of a HAR for 2D mesh networks are presented.
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