ACOR: Adaptive congestion-oblivious routing in dragonfly networks

Abstract

Low-diameter network topologies require non-minimal routing to avoid network congestion, such as Valiant routing. This increases base latency but avoids congestion issues. Optimized restricted variants focus on reducing path length. However, these optimizations only reduce paths for local traffic, where source and destination of each packet belong to the same partition of the network. This paper introduces ACOR: Adaptive Congestion-Oblivious Routing. ACOR leverages the restricted and recomputation mechanisms to reduce path length for local and global traffic, and extends it when the network conditions are adverse. ACOR relies on a sequence of misrouting policies ordered by path length. A hysteresis mechanism improves performance and avoids variability in the results. The ACOR mechanism can be combined with other non-minimal routing mechanism such as Piggyback. Results show that ACOR improves base latency in all cases, up to 28% standalone and up to 25.5% when combined with Piggyback, while requiring a simple implementation.