Resource Allocation in Time-Division-Multiplexed Networks on - purl PDF
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Resource Allocation in Time-Division-Multiplexed Networks on Chip Resource Allocation in Time-Division-Multiplexed Networks on Chip PROEFSCHRIFT terverkrijging vandegraadvandoctor aandeTechnischeUniversiteit Delft, opgezagvandeRectorMagnificusprof. ir. K.C.A.M.Luyben, voorzitter vanhetCollegevoorPromoties, inhetopenbaar teverdedigen opdinsdag24april2012om10.00uur door RaduS¸TEFAN MasterofScience Universitatea Transilvania Bras¸ov geboren teBras¸ov,Roemenie¨ Ditproefschrift isgoedgekeurd doordepromotor: Prof.dr.K.G.W.Goossens Samenstelling promotiecommissie: RectorMagnificus, voorzitter TechnischeUniversiteit Delft Prof. dr. K.G.W.Goossens, promotor TechnischeUniversiteit Delft Prof. dr. H.J.Sips TechnischeUniversiteit Delft Prof. dr. K.L.M.Bertels TechnischeUniversiteit Delft Prof. dr. R.H.J.M.Otten TechnischeUniversiteit Eindhoven Prof. dr. G.J.M.Smit UniversiteitTwente Dr. J.Flich Universidad Polite´cnicadeValencia ISBN:9789072298270 This dissertationis dedicatedtomy family, foralltheirunderstandingandsupportover theyears. Resource Allocation in Time-Division-Multiplexed Networks on Chip Radu STEFAN Abstract O ne of the challenges of engineering is to make the best possible use of the available resources, or in other words allocating the resources in such a way as to maximize the overall profit. In the context of networks on chip the resources are represented by the communication band- widthandthefinalprofitistheperformanceofanapplicationsupportedbythe networkonchip. Inthisthesiswefocusonnetworksonchipprovidingguaranteedperformance, i.e. guaranteeing for each application the delivery of a requested bandwidth. In these networks, hardware resources are allocated and assigned to each application for its entire lifetime. We discuss several solutions for delivering the allocated bandwidth, and we propose models which allow us to evaluate the performance of these solutions. Starting from a general, rate-based allo- cation model we gradually add more architectural restrictions that lower the implementation cost,butatthesametimesacrificesomeperformance. NoCs with allocation based on discrete rates are very common and include priority-based, TDM, SDM, FDM, and other NoCs. They all partition the bandwidth available on the network links into discrete units. In the case of TDMNoCsthese units are called timeslots. Theproblem ofresource alloca- tion inTDMNoCsconsists offinding paths through thenetwork between the nodes that wish to communicate, and selecting along these paths a set of free timeslotsthatissufficientlylargetofulfilltheapplication requirements. After allocation thebandwidth isguaranteed. Inthisthesis,wepropose,implementandevaluateallocationalgorithmsforall the proposed performance models. Particular effort is dedicated to allocation algorithms for the contention-free routing model, a restrictive, but low-cost form of TDM where allocation is particularly challenging. Our allocation algorithms deal both with spatial allocation, i.e., the selection of a specific path out of the available paths through the network, and temporal allocation, i i.e., along the time axis. The latter is used for optimizing bandwidth usage and latency which we will both discuss in depth. We propose two algorithms for the allocation of slots in the time domain, both of which we show to be optimal. We also demonstrate how the TDM schedule can be computed at run time, with low computational requirements. We demonstrate a system performing run-time allocation inFPGAandweimplement hardware acceleration forthe moreexpensive operations usedbytheallocation algorithm. WeproposeasynthesizableNoCimplementationbasedonthecontention-free- routingmodel,calleddAElite. Ourproposalusesexistingdesignflowsbuthas betterperformance andreducedhardwarecost. Thenetworksupports someof the less restrictive models that wehave previously introduced thus allowing a betterallocation ofresources. Finally, we present how the communication requests of the IPs are handled by the interconnect. We propose optimizations such as write coalescing and latency hiding techniques at the interface between IPs and the NoC and we demonstrate the performance benefits of the proposed approach in real appli- cations. The main conclusions of this thesis are that, compared to an ideal rate-based NoCofferingguaranteedbandwidth,introducingfixeddiscreteallocationunits causes a performance loss of 18% while using headers loses another 15%, under the considered, realistic scenarios. Other factors, such as topology, in- orderdelivery, etc. cause onlyaminorperformance loss. WefindÆthereal to lose46%comparedtoanidealrate-basednetwork,whilethedAElitenetwork introduced here loses less than 26% and is at the same time less expensive to implement. ii Acknowledgments I started my PhD under the supervision of Prof. Stamatis Vassiliadis who unfortunately fell ill soon afterwards and departed from among us one year later. Despite our very few encounters he had a strong influence on my development in the first years of my PhD. I would like to thank him as well as Prof. Georgi Gaydadjiev, Prof. Koen Bertels who were in charge of my supervision duringthattimeoftransition. IwouldliketothankmyPhDandpostdoctoralcolleaguesfortheirsupportand exchange ofideas. Ihopewewillremaininclosecontact inthefuture. I would like to thank my supervisor for his patience in reviewing the many iterations ofthisthesis. Lastbutnotleast,Iwouldliketothankyou,thereaderfortheinterestyouare showinginthiswork. R.Stefan Delft,TheNetherlands, 2010 iii
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