OBQA: Smart and cost-efficient queue scheme for Head-of-Line blocking elimination in fat-trees

High-speed interconnection networks are essential elements for different high-performance parallel-computing systems. One of the most common interconnection network topologies is the fat-tree, whose advantages have turned it into the favorite topology of many interconnect designers. One of these advantages is the possibility of using simple but efficient routing algorithms, like the recently proposed deterministic routing algorithm referred to as DET, which offers similar (or better) performance than Adaptive Routing while reducing complexity and guaranteeing in-order packet delivery. However, as other deterministic routing proposals, DET cannot react when packets intensely contend for network resources, leading to the appearance of Head-of-Line (HoL) blocking which spoils network performance. In this paper, we describe and evaluate a simple queue scheme that efficiently reduces HoL-blocking in fat-trees using the DET routing algorithm, without significantly increasing switch complexity and required silicon area. Additionally, we propose an implementation of OBQA in a feasible switch architecture.

► Head-of-Line (HoL) blocking spoils the lossless interconnection network performance.
► There are several HoL blocking reduction techniques, but they present some problems.
► OBQA is an HoL blocking reduction technique for Fat-Trees using deterministic routing.
► A feasible OBQA implementation is possible in Input-Queued Switch Architectures.
► OBQA is a cost-effective solution which notably reduces the HoL-blocking in fat-trees.