NoC design and optimization for Multi-core media processors

CHAPTER 3. LINK MICROARCHITECTURE EXPLORATION 31presents results on power-performance trade-off studies on Mesh, Torus, Folded Torus,Tree based network and a Reduced 2D Torus topologies by varying pipelining in links andfrequency and voltage scaling.The framework is used to study NoC designs of a CMP using different classes ofparallel computing benchmarks[6]. Traffic patterns from dense and sparse linear algebraapplicationsareusedinthisstudy. ThetrafficconsistsofbothRequest-Responsemessages(mimicking cache accesses) and One-Way messages. One of the key findings is that theaverage latency of a link can be reduced by increasing pipeline depth to a certain extent,as it enables link operation at higher link frequencies. There exists an optimum degree ofpipelining which minimizes the energy-delay product of the link.Using frequency scaling experiments we show that switching to a higher degree of linkpipelining to achieve higher frequency instead of adding larger buffers is advantageousfromapowerperspective. Twocasestudiescomparingtopologiesbasedonthroughputarepresented. A SystemC based simulation framework containing parameterizable routers,links, traffic generators and Sink nodes is used for NoC exploration.Organization of the ChapterRest of the chapter is organized as follows. A few router modelling, design space explorationandpowerestimationrelatedworkshavebeenintroducedinSection3.1.Adetailedliterature survey router modelling and design space exploration of NoCs had been presentedin Section 2.2 of Chapter 2. NoC exploration framework used in the trade-offstudies is described in Section 3.2. Latency, power, performance trade-offs, frequencyscaling and voltage scaling results for two case studies are presented in Sections 3.3 andSection 3.4. Section 3.3 presents design exploration results for 4×4 2 dimensional Mesh,a similar Torus and an equivalent Folded Torus NoC. Section 3.4 presents design explorationresults for a 16 node (4×4), Torus, Reduced Torus and a Tree based NoC. Resultsand findings are summarized in Section 3.5.