Hybrid Congestion Control for BXI-Based Interconnection Networks

Congestion threatens the performance of high-performance interconnection networks in Supercomputers and Data Centers, which has focused research attention in the last decades, resulting in many proposals for congestion control. The most successful ones involve either the use of traffic-injection throttling (e.g., DCQCN) to reduce the rate at which congesting flows are injected into the network, or the use of virtual channels (VCs) to separate congesting from non-congesting flows, thus reducing the main adverse effect of congestion: the head-of-line (HoL) blocking. In the first case, the rate reduction may be based on obsolete information about the network status, so the mechanism may overreact, underreact, or react too late. The second approach does not achieve a complete HoL blocking elimination. This paper proposes a combination of both approaches into a hybrid congestion control technique that uses VCs to separate congesting and non-congesting flows while, at the same time, throttling the injection of congesting flows at NICs when necessary. Our proposal can be applied to Ethernet-based switches, such as those being designed for the new version of the BXI network technology. However, our proposal can be applied to any switch architecture using buffers at both input and output ports. From the results of the simulation experiments run to evaluate our proposal, we can conclude that the hybrid technique significantly outperforms the congestion control solutions usually implemented in current Ethernet-based networks.