BST: A BookSim-Based Toolset to Simulate NoCs with Single- and Multi-Hop Bypass

Network-on-Chips are a critical part of modernmultiprocessors and their relevance will grow with the number ofcores. The development of future NoC designs relies on detailedsimulation models that accurately estimate their performance, power and hardware cost. Bypass routers are very relevant and promising proposals dueto their improved performance. Bypass routers reduce latencythanks to a combination of speculation, pre-routing (lookaheadrouting) and buffer bypass, which also reduce energy consumption by avoiding unnecessary buffer writes and reads. Multi-hop bypass NoCs, known as SMART, even bypass the crossbar of multiple routers in a single cycle. However, publicly available NoC simulators, such as BookSim or Garnet, do not implement bypass mechanisms or do not model them accurately. In this work, we present Bypass Simulation Toolset(BST), a set of tools to accurately simulate NoCs with single-and multi-hop bypass routers. BST combines and extends several simulation tools: an extension of BookSim with state-of-the-art cycle-accurate bypass router models and additional flow control mechanisms; an RTL implementation of multi-hop bypass mechanisms based on OpenSMART; an API to ease a modular integration of the BST NoC simulator in full system simulators; and a set of scripts to automate simulation execution and data collection. To showcase BST, we i) validate BookSim SMART models with the RTL implementation; ii) compare bypass and traditional non-bypass router models; iii) integrate BookSim in gem5 using the proposed API and compare it with gem5's Simple and Garnet 2.0 NoC models; and iv) present a case study evaluating different combinations of router types and topologies recently proposed for NoCs, highlighting the flexibility of the BST toolset. The toolset is available at www.atc.unican.es/software.html