Combining Source-adaptive and Oblivious Routing with Congestion Control in High-performance Interconnects using Hybrid and Direct Topologies

Abstract

Hybrid and direct topologies are cost-efficient and scalable options to interconnect thousands of end nodes in high-performance computing (HPC) systems. They offer a rich path diversity, high bisection bandwidth, and a reduced diameter guaranteeing low latency. In these topologies, efficient deterministic routing algorithms can be used to balance smartly the traffic flows among the available routes. Unfortunately, congestion leads these networks to saturation, where the HoL blocking effect degrades their performance dramatically. Among the proposed solutions to deal with HoL blocking, the routing algorithms selecting alternative routes, such as adaptive and oblivious, can mitigate the congestion effects. Other techniques use queues to separate congested flows from non-congested ones, thus reducing the HoL blocking. In this article, we propose a new approach that reduces HoL blocking in hybrid and direct topologies using source-adaptive and oblivious routing. This approach also guarantees deadlock-freedom as it uses virtual networks to break potential cycles generated by the routing policy in the topology. Specifically, we propose two techniques, called Source-Adaptive Solution for Head-of-Line Blocking Avoidance (SASHA) and Oblivious Solution for Head-of-Line Blocking Avoidance (OSHA). Experiment results, carried out through simulations under different traffic scenarios, show that SASHA and OSHA can significantly reduce the HoL blocking.