Evaluation of congestion detection mechanisms for InfiniBand switches

InfiniBand System Area Networks using link-level flow control can experience congestion spreading, where one bottleneck link causes traffic to block throughout the network. End-to-end congestion control using Explicit Congestion Notification (ECN) packet marking has the potential to solve this problem. In this paper, we develop and evaluate ECN mechanisms for switches with input-buffered configuration (typical for InfiniBand), as opposed to traditional techniques that target output-buffered switches. Our mechanisms vary in two dimensions: the condition that triggers a marking event, and the set of packets marked at such an event. The experimental results show that our approaches avoid congestion spreading while preserving high network throughput. In addition, selective marking of packets at an input buffers on each marking event provides better fairness than a naive mechanism that marks only packets in a full input buffer. Finally, schemes that use state at both input and output ports to trigger marking events can improve fairness over purely input-triggered marking schemes.