Efficient Congestion Management for High-Speed Interconnects using Adaptive Routing

The interconnection network is the central element in high-performance computing (HPC) clusters and Datacenters, where thousands of end nodes must communicate in a fast and reliable manner. The network performance depends on several design choices, such as the topology, the routing algorithm, the switch architecture, etc. Highly efficient routing algorithms, either deterministic or adaptive, have been proposed to smartly balance traffic flows in cost-effective network topologies, but their performance is reduced in scenarios where congestion and their negative effects (e.g. the HoL blocking) appear. In particular, in scenarios where congestion is intense and persistent, the HoL blocking may degrade dramatically the performance of adaptive routing algorithms, since they may spread congested traffic flows through all the available routes. In addition, as we have shown in previous studies, this spreading of congested flows may spoil the performance of the static queuing schemes that are used to reduce HoL blocking by separating flows into different queues at switch buffers. Indeed, as these schemes are based on a static criterion defined prior to the traffic injection in the network, they are unable to avoid that congested and non-congested flows share queues when paired with adaptive routing. In this paper, we propose to use some existing static queuing schemes and dynamic allocation of virtual channels (VCs) to isolate into a single VC the flows whose routes have been adaptively routed, in order to prevent the impact of the congestion spreading through several routes. Basically, adapted flows are moved to a special adapted-flow channel (AFC), so that they do not interact with flows mapped to other VCs by the static queuing scheme. In this way, the HoL blocking that adaptively routed flows could cause to non-adaptive flows is prevented, even if congested flows have been spread through several routes. On the other hand, the static queuing scheme will reduce without any interference the HoL blocking that may appear among non-adaptive flows. To evaluate our proposal we have conducted extensive simulation experiments modeling large interconnection networks based on the fat-tree topology. From the obtained results, we can conclude that our approach efficiently and significantly reduces the HoL blocking impact in interconnection networks using adaptive routing and queuing schemes when congestion appears.