On chip interconnects for multiprocessor turbo decoding architectures

International audienc

Efficient bypass mechanisms for low latency networks on-chip

RESUMEN: La importancia de las redes en-chip en los procesadores multi-núcleo es cada vez mayor. Los routers con baipás son una solución eficiente para reducir la latencia de estas redes. Existen dos tipos de redes con baipás: single-hop y multi-hop. Las redes con baipás single-hop minimizan la latencia individual de cada router al asignar los recursos del router con antelación a la recepción de los paquetes. Las redes con baipás multi-hop, conocidas como SMART, permiten que los paquetes atraviesen múltiples routers en un único ciclo. La primera propuesta de esta tesis es Non-Empty Buffer Bypass (NEBB), un mecanismo que incrementa la utilización del baipás de tipo single-hop, eliminando la necesidad de usar canales virtuales. Para redes con baipás multi-hop propone SMART++ y S-SMART++. SMART++ elimina la necesidad de SMART de usar una gran cantidad de canales virtuales para aprovechar el ancho de banda de la red, permitiendo el diseño de configuraciones de bajo coste. S-SMART++ hace uso de la asignación de recursos de forma especulativa para preparar el baipás de tipo multi-hop. Este mecanismo reduce la latencia y su dependencia con la longitud máxima de los saltos de tipo multi-hop, aspecto clave para su viabilidad en diseños reales. La contribución final es un conjunto de herramientas de código abierto llamada Bypass Simulation Toolset (BST) compuesto por versiones extendidas de BookSim y OpenSMART, una API para integrar BookSim en otros simuladores y una serie de scripts para facilitar el diseño y evaluación de este tipo de redes.ABSTRACT: Networks on-Chip (NoCs) are becoming more important in many-core processors as the number of cores grows. Bypass routers are an efficient solution that skips pipeline stages. There are two types of bypass mechanisms: single-hop and multi-hop bypass. Single-hop bypass minimizes the router delay by skipping allocation stages in each hop. Multi-hop bypass, called SMART, minimizes the effective number of hops by traversing multiple routers in a single cycle. The first proposal of this dissertation is Non-Empty Buffer Bypass (NEBB) for single-hop bypass, which increases the bypass utilization without requiring VCs to match traditional bypass routers. It proposes SMART++ and S-SMART++ for multi-hop bypass. SMART++ removes the requirement of using multiple VCs of SMART to exploit the bandwidth of the network, enabling low-cost configurations. S-SMART++ relies on speculative allocation to set up multi-hop bypass paths. Thus, it reduces latency and its dependency with the maximum length of multi-hops, relaxing the requirements to integrate multi-hop bypass in real designs. The final contribution is an open-source set of tools to simulate bypass NoCs called Bypass Simulation Toolset (BST) conformed by extended versions of BookSim and OpenSMART, an API to integrate BookSim in other simulators, and scripts to simplify the designing and evaluation of such NoCs.This work was supported by the Spanish Ministry of Science, Innovation and Universities, FPI grant BES-2017-079971, and contracts TIN2010-21291-C02-02, TIN2013- 46957-C2-2-P, TIN2015-65316-P, TIN2016-76635-C2-2-R (AEI/FEDER, UE) and TIC PID2019-105660RB-C22; the European HiPEAC Network of Excellence; the European Community's Seventh Framework Programme (FP7/2007-2013), under the Mont-Blanc 1 and 2 projects (grant agreements n 288777 and 610402); the European Union's Horizon 2020 research and innovation programme under the Mont-Blanc 3 project (grant agreement nº 671697). Bluespec Inc. provided access to Bluespec tools

An Energy and Performance Exploration of Network-on-Chip Architectures

In this paper, we explore the designs of a circuit-switched router, a wormhole router, a quality-of-service (QoS) supporting virtual channel router and a speculative virtual channel router and accurately evaluate the energy-performance tradeoffs they offer. Power results from the designs placed and routed in a 90-nm CMOS process show that all the architectures dissipate significant idle state power. The additional energy required to route a packet through the router is then shown to be dominated by the data path. This leads to the key result that, if this trend continues, the use of more elaborate control can be justified and will not be immediately limited by the energy budget. A performance analysis also shows that dynamic resource allocation leads to the lowest network latencies, while static allocation may be used to meet QoS goals. Combining the power and performance figures then allows an energy-latency product to be calculated to judge the efficiency of each of the networks. The speculative virtual channel router was shown to have a very similar efficiency to the wormhole router, while providing a better performance, supporting its use for general purpose designs. Finally, area metrics are also presented to allow a comparison of implementation costs

On Fault Tolerance Methods for Networks-on-Chip

Technology scaling has proceeded into dimensions in which the reliability of manufactured devices is becoming endangered. The reliability decrease is a consequence of physical limitations, relative increase of variations, and decreasing noise margins, among others. A promising solution for bringing the reliability of circuits back to a desired level is the use of design methods which introduce tolerance against possible faults in an integrated circuit. This thesis studies and presents fault tolerance methods for network-onchip (NoC) which is a design paradigm targeted for very large systems-onchip. In a NoC resources, such as processors and memories, are connected to a communication network; comparable to the Internet. Fault tolerance in such a system can be achieved at many abstraction levels. The thesis studies the origin of faults in modern technologies and explains the classification to transient, intermittent and permanent faults. A survey of fault tolerance methods is presented to demonstrate the diversity of available methods. Networks-on-chip are approached by exploring their main design choices: the selection of a topology, routing protocol, and flow control method. Fault tolerance methods for NoCs are studied at different layers of the OSI reference model. The data link layer provides a reliable communication link over a physical channel. Error control coding is an efficient fault tolerance method especially against transient faults at this abstraction level. Error control coding methods suitable for on-chip communication are studied and their implementations presented. Error control coding loses its effectiveness in the presence of intermittent and permanent faults. Therefore, other solutions against them are presented. The introduction of spare wires and split transmissions are shown to provide good tolerance against intermittent and permanent errors and their combination to error control coding is illustrated. At the network layer positioned above the data link layer, fault tolerance can be achieved with the design of fault tolerant network topologies and routing algorithms. Both of these approaches are presented in the thesis together with realizations in the both categories. The thesis concludes that an optimal fault tolerance solution contains carefully co-designed elements from different abstraction levelsSiirretty Doriast

Design Methods and Tools for Application-Specific Predictable Networks-on-Chip

As the complexity of applications grows with each new generation, so does the demand for computation power. To satisfy the computation demands at manageable power levels, we see a shift in the design paradigm from single processor systems to Multiprocessor Systems-on-Chip (MPSoCs). MPSoCs leverage the parallelism in applications to increase the performance at the same power levels. To further improve the computation to power consumption ratio, MPSoCs for embedded applications are heterogeneous and integrate cores that are specialized to perform the different functionalities of the application. With technology scaling, wire power consumption is increasing compared to logic, making communication as expensive as computation. Therefore customizing the interconnect is necessary to achieve energy efficiency. Designing an optimal application specific Network-on-Chip (NoC), that meets application demands, requires the exploration of a large design space. Automatic design and optimization of the NoC is required in order to achieve fast design closure, especially for heterogeneous MPSoCs. To continue to meet the computation requirements of future applications new technologies are emerging. Three dimensional integration promises to increase the number of transistors by stacking multiple silicon layers. This will lead to an increase in the number of cores of the MPSoCs resulting in increased communication demands. To compensate for the increase in the wire delay in new technology nodes as well as to reduce the power consumption further, multi-synchronous design is becoming popular. With multiple clock signals, different parts of the MPSoC can be clocked at different frequencies according to the current demands of the application and can even be shutdown when they are not used at all. This further complicates the design of the NoC.Many applications require different levels of guarantee from the NoC in order to perform their functionality correctly. As communication traffic patterns become more complex, the performance of the NoC can no longer be predicted statically. Therefore designing the interconnect network requires that such guarantees are provided during the dynamic operation of the system which includes the interaction with major subsystems (i.e., main memory) and not just the interconnect itself. In this thesis, I present novel methods to design application-specific NoCs that meet performance demands, under the constraints of new technologies. To provide different levels of Quality of Service, I integrate methods to estimate the NoC performance during the design phase of the interconnect topology. I present methods and architectures for NoCs to efficiently access memory systems, in order to achieve predictable operation of the systems from the point of view of the communication as well as the bottleneck target devices. Therefore the main contribution of the thesis is twofold: scientific as I propose new algorithms to perform topology synthesis and engineering by presenting extensive experiments and architectures for NoC design

A distributed interleaving scheme for efficient access to WideIO DRAM memory

Achieving the main memory (DRAM) required bandwidth at acceptable power levels for current and future applications is a major challenge for System-on-Chip designers for mobile platforms. Three dimensional (3D) integration and 3D stacked DRAM memories promise to provide a significant boost in bandwidth at low power levels by exploiting multiple channels and wide data interfaces. In this paper, we address the problem of efficiently exploiting the multiple channels provided by standard (JEDEC’s WIDEIO) 3D-stacked memories, to extract maximal effective bandwidth and minimize latency for main memory access. We propose a new distributed interleaved access method that leverages the on-chip interconnect to simplify the design and implementation of the DRAM controller, without impacting performance compared to traditional centralized implementations. We perform experiments on realistic workload for a mobile communication and multimedia platform and show that our proposed distributed interleaving memory access method improves the overall throughput while minimally impacting the performance of latency sensitive communication flows

Performance Implications of NoCs on 3D-Stacked Memories: Insights from the Hybrid Memory Cube

Memories that exploit three-dimensional (3D)-stacking technology, which integrate memory and logic dies in a single stack, are becoming popular. These memories, such as Hybrid Memory Cube (HMC), utilize a network-on-chip (NoC) design for connecting their internal structural organizations. This novel usage of NoC, in addition to aiding processing-in-memory capabilities, enables numerous benefits such as high bandwidth and memory-level parallelism. However, the implications of NoCs on the characteristics of 3D-stacked memories in terms of memory access latency and bandwidth have not been fully explored. This paper addresses this knowledge gap by (i) characterizing an HMC prototype on the AC-510 accelerator board and revealing its access latency behaviors, and (ii) by investigating the implications of such behaviors on system and software designs