Dragonfly networks have a two-level hierarchical arrangement of the network routers, and allow for a competitive cost-performance solution in large systems. Non-minimal adaptive routing is employed to fully exploit the path diversity and increase the performance under adversarial traffic patterns. Throughput unfairness prevents a balanced use of the resources across the network nodes and degrades severely the performance of any application running on an affected node. Previous works have demonstrated the presence of throughput unfairness in Dragonflies under certain adversarial traffic patterns, and proposed different alternatives to effectively combat such effect. In this paper we introduce a new traffic pattern denoted adversarial consecutive (ADVc), which portrays a real use case, and evaluate its impact on network performance and throughput fairness. This traffic pattern is the most adversarial in terms of network fairness. Our evaluations, both with or without transitover-injection priority, show that global misrouting policies do not properly alleviate this problem. Therefore, explicit fairness mechanisms are required for these networks.

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 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