Advances in CMOS-compatible photonic elements have made it plausible to exploit nanophotonic communications to overcome the limitations of traditional NoCs. Amongst various proposed nanophotonic architectures, optical crossbars have been shown to provide high performance in terms of bandwidth and latency. In general, optical crossbars provide a vast volume of network resources that are shared among all the cores within the chip. In this paper, we present a fair and efficient admission control mechanism for shared wavelengths and buffer space in optical crossbars. We model buffer management and wavelength assignment as a utility-based convex optimization problem, whose solution determines the admission control policy. Thanks to efficient convex optimization techniques, we obtain the globally optimal solution of the admission control optimization problem by using simple and yet efficient iterative algorithms. We cast our solution procedure as an iterative algorithm to be implemented a central admission controller. Our experimental results corroborate the gain that can be obtained by using such an admission controller to manage the shared resources of the system. Furthermore, they confirm that the proposed admission control algorithm works well for various traffic patterns and parameters, and evinces a tractable scalability with increase in the number of cores of the crossbar.
Various approaches have been proposed to exploit nanophotonics for on-chip communication networks. Development of efficient optical data buffers is still a challenging problem, which makes it quite hard to construct a fully optical packet-switched network. As a result, @cite_9 propose a hybrid approach, in which large data packets are transferred using an optical circuit-switched network whereas the optical network is controlled by an electronic packet-switched network. @cite_43 consider the architecture proposed in @cite_9 and propose a predictive switching and reservation technique to reduce its path setup latency. In some other hybrid architectures such as @cite_10 , local communications are carried out by an electrical network, whereas long distance communications utilize optical links. @cite_13 exploit non-blocking photonic switches as well as light-weight electronic routers to decrease the latency and power overheads of hybrid architectures. Garc ' i a- @cite_4 propose a set of policies to manage hybrid networks consisting of ring-based photonic and electrical mesh sub-networks. The proposed policies use different criteria, such as message size, distance, and photonic ring availability, to decide which sub-network to be used for each message.
@cite_4 @cite_10 @cite_9 @cite_43 @cite_13
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SUMMARY Nanophotonics promises to solve the scalability problems of current electrical interconnects thanks to its low sensitivity to distance in terms of latency and energy consumption. Before this technology reaches maturity, hybrid photonic-electronic networks will be a viable alternative. Ideally, ordinary electrical meshes and ring-based photonic networks should cooperate to minimize overall latency and energy consumption, but currently, we lack mechanisms to do this efficiently. In this paper, we present novel fine-grain policies to manage the photonic resources in a tiled chip multiprocessor (CMP) scenario. Our policies are dynamic and base their decisions on parameters such as message size, ring availability, and distance between endpoints, at the message level. The resulting network behavior is also fairer to all cores, reducing processor idle time thanks to faster thread synchronization. All these policies improve performance when compared to the same CMP without the photonic ring, and the most elaborate ones reduce the overall network latency by 50 , execution time by 36 , and network energy consumption by 52 on average, in a 16-core CMP for the PARSEC benchmark suite. Larger hybrid networks with 64 endpoints for 256-core CMPs, based on Corona and Firefly designs, also show far superior throughput and lower latency if managed by one of the proposed policies. Copyright © 2014 John Wiley & Sons, Ltd. To meet energy-efficient performance demands, the computing industry has moved to parallel computer architectures, such as chip multiprocessors (CMPs), internally interconnected via networks-on-chip (NoC) to meet growing communication needs. Achieving scaling performance as core counts increase to the hundreds in future CMPs, however, will require high performance, yet energy-efficient interconnects. Silicon nanophotonics is a promising replacement for electronic on-chip interconnect due to its high bandwidth and low latency, however, prior techniques have required high static power for the laser and ring thermal tuning. We propose a novel nano-photonic NoC (PNoC) architecture, LumiNOC, optimized for high performance and power-efficiency. This paper makes three primary contributions: a novel, nanophotonic architecture which partitions the network into subnets for better efficiency; a purely photonic, in-band, distributed arbitration scheme; and a channel sharing arrangement utilizing the same waveguides and wavelengths for arbitration as data transmission. In a 64-node NoC under synthetic traffic, LumiNOC enjoys 50 lower latency at low loads and @math higher throughput per Watt on synthetic traffic, versus other reported PNoCs. LumiNOC reduces latencies @math versus an electrical 2-D mesh NoCs on the PARSEC shared-memory, multithreaded benchmark suite. Future chip multi-processors (CMPs) will require high-performance yet low-energy networks-on-chip to provide scalable communication for the increasing number of cores. CMOS-compatible nanophotonic interconnects have recently emerged as a promising candidate for replacing traditional electrical network-on-chip, by providing high bandwidth chip-wide communication at low latency and power. In this paper, we utilize the emerging nanophotonic technology and propose RCBus, an optical network-on-chip topology in which multiple nanophotonic buses are uniformly distributed in each row and column of a two-dimensional torus network. Each bus employs a dense-wavelength-division-multiplexing optical waveguide to enable high-bandwidth express traversal along each dimension. We use multiple write single-read schemes and virtual channel based token protocol to implement light-speed arbitration and flow control. The optical-electrical interface is also studied in the paper. The proposed optical network-on-chip can exploit the advantages of both photonic bus and direct torus topology. Simulation results under synthetic and real-world application traffic show that RCBus is 2X better in terms of performance than the electrical mesh network-on-chip while saving nearly 30 power, and achieves on average 24 throughput improvement at much lower cost compared to the state-of-the-art optical network. DOI: http: dx.doi.org 10.5755 j01.eee.18.8.2633 The potential advantages of optics at high link speeds have led to significant interest in deploying optical switching technology in data-center networks. Initial efforts have focused on hybrid approaches that rely on millisecond-scale circuit switching in the core of the network, while maintaining the flexibility of electrical packet switching at the edge. Recent demonstrations of microsecond-scale optical circuit switches motivate considering circuit switching for more dynamic traffic such as that generated from a top-of-rack (ToR) switch. Based on these technology trends, we propose a prototype hybrid ToR, called REACToR, which utilizes a combination of packet switching and circuit switching to appear to end-hosts as a packet-switched ToR. In this paper, we describe a prototype REACToR control plane which synchronizes end host transmissions with end-to-end circuit assignments. This control plane can react to rapid, bursty changes in the traffic from end hosts on a time scale of 100s of microseconds, several orders of magnitude faster than previous hybrid approaches. Using the experimental data from a system of eight end hosts, we calibrate a hybrid network simulator and use this simulator to predict the performance of larger-scale hybrid networks.