Latency-driven Optimization of Switching Pipeline Design in Network Chips

Abstract

A network switch implements multiple services and each service is formed by a number of match-action operations through several pipeline stages. These services running in the switch equipment are to process various packets based on standard internet protocols to decide the route of each packet. Data packets come in serial to a port, where each packet is processed by a service according to the contents of the packet headers and then send out via another port. Design of the switch, i.e., mapping services to physical resources in the pipeline stages, aims to achieve low switching latency with small chip area while respecting data-flow dependencies and hardware constraints. The current practice relies on expertise of engineers empirically, which is laborious and generates mediocre results. In this paper, we propose a switching pipeline design optimizatton technique, called SPOT. Our main contributions are as follows: (i) We first formulate the bi-objective (latency and chip area) constrained design optimization problem; (ii) SPOT quickly spots a feasible solution from a largely unfeasible design space using a dependency-aware greedy algorithm; (iii) Based on the above feasible seed, SPOT explores the design space with hundreds of decision dimensions towards Pareto optimal solutions using non-dominated sorting genetic algorithm II (NSGA-II) and multi-objective tabu search (MOTS), both adapted to be deployed in this problem setting. We apply SPOT on three sets of real-world network services. In comparison to the design sheets prepared by expert engineers, experiments show that SPOT offers 20.63% shorter service latency and 4.55% smaller chip area on average. As a by-product, the power consumption is lowered by 23.72% on average, which is correlated to the chip area. For hard real-time scenarios, the longest service latency a data packet may experience is the major concern. SPOT reduces the worst-case service latency by 12.65% on average. SPOT is the first automated optimization solution for switching pipeline design in network chips, being utilized in millions of network products of various kinds and saving manual efforts from days to minutes.