Maurizio Palesi

Implementation and Analysis of a New Selection Strategy for Adaptive Routing in Networks-on-Chip

Efficient and deadlock-free routing is critical to the performance of networks-on-chip. The effectiveness of any adaptive routing algorithm strongly depends on the underlying selection strategy. A selection function is used to select the output channel where the packet will be forwarded on. In this paper we present a novel selection strategy that can be coupled with any adaptive routing algorithm. The proposed selection strategy is based on the concept of Neighbors-on-Path the aims of which is to exploit the situations of indecision occurring when the routing function returns several admissible output channels. The overall objective is to choose the channel that will allow the packet to be routed to its destination along a path that is as free as possible of congested nodes. Performance evaluation is carried out by using a flit-accurate simulator under traffic scenarios generated by both synthetic and real applications. Results obtained show how the proposed selection strategy applied to the Odd-Even routing algorithm yields an improvement in both average delay and saturation point up to 20% and 30% on average respectively, with a minimal overhead in terms of area occupation. In addition, a positive effect on total energy consumption is also observed under near-congestion packet injection rates.

Multi-objective design space exploration using genetic algorithms

In this work, we provide a technique for efficiently exploring a parameterized system-on-a-chip (SoC) architecture to find all Pareto-optimal configurations in a multi-objective design space. Globally, our approach uses a parameter dependency model of our target parameterized SoC architecture to extensively prune non-optimal subspaces. Locally, our approach applies genetic algorithms (GAs) to discover Pareto-optimal configurations within the remaining design points. The computed Pareto-optimal configurations will represent the range of performance (e.g., timing and power) tradeoffs that are obtainable by adjusting parameter values for a fixed application that is mapped on the parameterized SoC architecture. We have successfully applied our technique to explore Pareto-optimal configurations for a number of applications mapped on a parameterized SoC architecture.

Application Specific Routing Algorithms for Networks on Chip

In this paper we present a methodology to develop efficient and deadlock free routing algorithms for Network-on-Chip (NoC) platforms which are specialized for an application or a set of concurrent applications. The proposed methodology, called application specific routing algorithm (APSRA), exploits the application specific information regarding pairs of cores which communicate and other pairs which never communicate in the NoC platform to maximize communication adaptivity and performance. The methodology also exploits the known information regarding concurrency/non-concurrency of communication transactions among cores for the same purpose. We demonstrate, through analysis of adaptivity as well as simulation based evaluation of latency and throughput, that algorithms produced by the proposed methodology give significantly higher performance as compared to other deadlock free algorithms for both homogeneous as well as heterogeneous 2D mesh topology NoC systems. For example, for homogeneous mesh NoC, APSRA results in approximately 30% less average delay as compared to odd-even algorithm just below saturation load. Similarly the saturation load point for APSRA is significantly higher as compared to other adaptive routing algorithms for both homogeneous and non-homogeneous mesh networks.

Efficient design space exploration for application specific systems-on-a-chip

A reduction in the time-to-market has led to widespread use of pre-designed parametric architectural solutions known as system-on-a-chip (SoC) platforms. A system designer has to configure the platform in such a way as to optimize it for the execution of a specific application. Very frequently, however, the space of possible configurations that can be mapped onto a SoC platform is huge and the computational effort needed to evaluate a single system configuration can be very costly. In this paper we propose an approach which tackles the problem of design space exploration (DSE) in both of the fronts of the reduction of the number of system configurations to be simulated and the reduction of the time required to evaluate (i.e., simulate) a system configuration. More precisely, we propose the use of Multi-objective Evolutionary Algorithms as optimization technique and Fuzzy Systems for the estimation of the performance indexes to be optimized. The proposed approach is applied on a highly parameterized SoC platform based on a parameterized VLIW processor and a parameterized memory hierarchy for the optimization of performance and power dissipation. The approach is evaluated in terms of both accuracy and efficiency and compared with several established DSE approaches. The results obtained for a set of multimedia applications show an improvement in both accuracy and exploration time.

A methodology for design of application specific deadlock-free routing algorithms for NoC systems

In this paper, we present a methodology to specialize the routing algorithm in routing table based NoC routers. It tries to maximize the communication performance while ensuring deadlock free routing for an application. We demonstrate through analysis that routing algorithms generated by our methodology have higher adaptiveness as compared to turn-model based deadlock free routing algorithms for a mesh topology NoC architecture. Performance evaluation is carried out by using a flit-accurate simulator on traffic scenarios generated by both synthetic and real applications. The routing algorithms generated by the proposed methodology achieve an improvement in delay close to 50% and 30% over deterministic XY routing algorithm and adaptive odd-even routing algorithm respectively.

Noxim: An open, extensible and cycle-accurate network on chip simulator

Emerging on-chip communication technologies like wireless Networks-on-Chip (WiNoCs) have been proposed as candidate solutions for addressing the scalability limitations of conventional multi-hop NoC architectures. In a WiNoC, a subset of network nodes are equipped with a wireless interface which allows them long-range communication in a single hop. This paper presents Noxim, an open, configurable, extendible, cycle-accurate NoC simulator developed in SystemC which allows to analyze the performance and power figures of both conventional wired NoC and emerging WiNoC architectures.

HARAQ: Congestion-Aware Learning Model for Highly Adaptive Routing Algorithm in On-Chip Networks

The occurrence of congestion in on-chip networks can severely degrade the performance due to increased message latency. In mesh topology, minimal methods can propagate messages over two directions at each switch. When shortest paths are congested, sending more messages through them can deteriorate the congestion condition considerably. In this paper, we present an adaptive routing algorithm for on-chip networks that provide a wide range of alternative paths between each pair of source and destination switches. Initially, the algorithm determines all permitted turns in the network including 180-degree turns on a single channel without creating cycles. The implementation of the algorithm provides the best usage of all allowable turns to route messages more adaptively in the network. On top of that, for selecting a less congested path, an optimized and scalable learning method is utilized. The learning method is based on local and global congestion information and can estimate the latency from each output channel to the destination region.

Data Encoding Schemes in Networks on Chip

An ever more significant fraction of the overall power dissipation of a network-on-chip (NoC) based system-on-chip (SoC) is due to the interconnection system. In fact, as technology shrinks, the power contribute of NoC links starts to compete with that of NoC routers. In this paper, we propose the use of data encoding techniques as a viable way to reduce both power dissipation and energy consumption of NoC links. The proposed encoding scheme exploits the wormhole switching techniques and works on an end-to-end basis. That is, flits are encoded by the network interface (NI) before they are injected in the network and are decoded by the destination NI. This makes the scheme transparent to the underlying network since the encoder and decoder logic is integrated in the NI and no modification of the routers architecture is required. We assess the proposed encoding scheme on a set of representative data streams (both synthetic and extracted from real applications) showing that it is possible to reduce the power contribution of both the self-switching activity and the coupling switching activity in inter-routers links. As results, we obtain a reduction in total power dissipation and energy consumption up to 37% and 18%, respectively, without any significant degradation in terms of both performance and silicon area.

Routing Algorithms in Networks-on-Chip

This book provides a single-source reference to routing algorithms for Networks-on-Chip (NoCs), as well as in-depth discussions of advanced solutions applied to current and next generation, many core NoC-based Systems-on-Chip (SoCs). After a basic introduction to the NoC design paradigm and architectures, routing algorithms for NoC architectures are presented and discussed at all abstraction levels, from the algorithmic level to actual implementation. Coverage emphasizes the role played by the routing algorithm and is organized around key problems affecting current and next generation, many-core SoCs. A selection of routing algorithms is included, specifically designed to address key issues faced by designers in the ultra-deep sub-micron (UDSM) era, including performance improvement, power, energy, and thermal issues, fault tolerance and reliability.

Neighbors-on-Path: A New Selection Strategy for On-Chip Networks

Efficient and deadlock-free routing is critical to the performance of networks-on-chip. In this paper we present an approach that can be coupled to any adaptive routing algorithm to improve the performance with a minimal overhead on area and energy consumption. The proposed approach introduces the concept of neighbors-on-path to exploit the situations of indecision occurring when the routing function returns several admissible output channels. A selection strategy is developed with the aim to choose the channel that will allow the packet to be routed to its destination along a path that is as free as possible of congested nodes. Performance evaluation is carried out by using a flit-accurate simulator on traffic scenarios generated by both synthetic and real applications. Results obtained show how the proposed selection policy applied to the odd-even routing algorithm outperforms other deterministic and adaptive routing algorithms both in average delay and energy consumption