Adaptive routing is an efficient congestion avoidance mechanism for modern Datacenter and HPC networks. Congestion detection traditionally relies on the occupancy of the router queues. However, this approach can hinder performance due to coarse-grain measurements with small buffers, and potential routing oscillations with large buffers. We introduce an alternative mechanism, labelled Contention-Based Adaptive Routing. Our mechanism adapts routing based on an estimation of “network contention”, the simultaneity of traffic flows contending for a network port. Our system employs a set of counters which track the demand for each output port. This exploits path diversity thanks to earlier detection of adversarial traffic patterns, and decouples buffer size and queue occupancy from contention detection. We evaluate our mechanism in a Dragonfly network. Our evaluations show this mechanism achieves optimal latency under uniform traffic and similar to best previous routing mechanisms under adversarial patterns, with immediate adaptation to traffic pattern changes.

This work has been supported by the Spanish Ministry of Education, FPU grant FPU13/00337, the Spanish Science and Technology Commission (CICYT) under contracts TIN2012-34557 and TIN2013-46957-C2-2-P, the European Union FP7 under Agreement ICT-288777 (Mont-Blanc) and ERC-321253 (RoMoL), the European HiPEAC Network of Excellence, and the JSA no. 2013-119 as part of the IBM/BSC Technology Center for Supercomputing agreement.

Peer Reviewed