Global misrouting policies in two-level hierarchical networks

Dragonfly networks are composed of interconnected groups of routers. Adaptive routing allows packets to be forwarded minimally or non-minimally adapting to the traffic conditions in the network. While minimal routing sends traffic directly between groups, non-minimal routing employs an intermediate group to balance network load. A random selection of this intermediate group (denoted as RRG) typically implies an extra local hop in the source group, what increases average path length and can reduce performance. In this paper we identify different policies for the selection of such intermediate group and explore their performance. Interestingly, simulation results show that an eager policy (denoted as CRG) that selects the intermediate group only between those directly connected to the ongoing router causes starvation in some network nodes. On the contrary, the best performance is obtained by a by a \mixed mode" policy (denoted as MM) that adds a local hop when the packet has moved away from the source router