Seeds for a Heterogeneous Interconnect

Traditionally, a parallel application is partitioned, mapped and then routed on a network of compute nodes where the topology of the interconnection network is known beforehand and is homogeneous. However, such homogeneity in interconnects is rarely required or needed for several important classes of applications. Nevertheless such interconnects are designed this way, i.e., with redundant links, to accommodate the communication patterns of a wide range of applications. However, with recent advances in technology for optical circuit switches, it is now possible to construct network with much fewer links, and to make the link endpoints configurable to suit the communication pattern of a given application. While this is economical (saving both links and the power to run them), it raises the difficult problem of how to configure the network and how to reconfigure it quickly when the application's communication pattern changes. Since the space of all configurable topologies is large and determining the quality of a topology is a time-consuming process, it is not feasible to explore the entire space. One way of dealing with this limitation is to start the search from a ``good'' initial topology and then conduct a restricted search around it. The success of such a strategy crucially depends on the choice of the initial or seed topology. In the past, such an initial topology was computed by mimicking the communication requirements of the application. In this paper, we propose a different approach by showing that interconnect topologies such as chordal rings(circulant graphs) chosen based on metrics such as bisection width and average shortest path length can provide a better starting point. The topology obtained by searching around such an initial topology provides almost as good a performance as an application-specific initial topology, and the search time is significantly reduced.