Adaptive Wormhole Routing Research Articles

Fully Reliable Dynamic Routing Logic for a Fault-Tolerant NoC Architecture

A fault-tolerant adaptive wormhole routing function for Networks-on-Chips (NoCs) is presented. The novelty of this routing logic is that it is capable of using runtime information on availability of links to dynamically bypass faulty channels. When faults occur, no offline reconfiguration or dropping of packets is necessary. Instead, dynamic routes are suggested on-the-fly. Routing decisions are based only on local knowledge, which allows for fast switching. Our approach does not use any costly virtual channels. As we do not prohibit cyclic dependencies, the routing function provides minimal routing from source to destination even in the presence of faults. We have implemented the architecture design using synthesizable HDL. Using simulations, we have assessed the overhead of our approach in terms of latency, power and area. On average, even with 40% of the links faulty our routing logic is capable performing correctly. Using formal verification, we have proven 100% reliability up to three faults, i.e., for any combination of three faults our routing logic remains connected, deadlock-free and livelock-free.

Probabilistic odd–even: an adaptive wormhole routing algorithm for 2D mesh network-on-chip

Wormhole routing is a popular routing technique used in network-on-chip. It is efficient but susceptible to deadlock, while deadlock will significantly degrade the network performance of NoC. Most existing adaptive wormhole routings avoid deadlock by reducing the degree of adaptiveness and thus sacrificing network performance. In this paper, we address both deadlock and network performance issues jointly, and propose a probabilistic odd---even (POE) routing algorithm that achieves the minimum packet delivery delay. The proposed POE dynamically adjusts the probabilities of constrained turns that may lead to deadlocks according to the current network conditions, and uses an efficient deadlock detection and recovery scheme when a deadlock happens. By adopting constrained turns adaptively to the network status, it not only reduces the frequency of deadlock and allows the network to be swiftly recovered when it occurs, but also greatly improves the degree of adaptiveness to obtain high network performance. Experimental results show that our method achieves a significant performance improvement both in terms of network throughput and average packet latency compared with the existing methods such as XY, odd---even, abacus turn model and fully adaptive routing algorithm while it only has moderate energy consumption.

Parallel photon-mapping rendering on a mesh-NoC-based MPSoC platform

High demand 3-D scenes on embedded systems draw the developers’ attention to use the whole resources of current low-power processors and add dedicated hardware as a graphic accelerator unit to deal with real-time realistic scene rendering. Photon mapping, as one of the most powerful techniques to render highly realistic 3-D images by high amounts of floating-point operations, is very time-consuming. To use the advantages of multiprocessor systems to make 3-D scenes, parallel photon-mapping rendering on a homogeneous multiprocessor SoC (MPSoC) platform along with a mesh NoC by an adaptive wormhole routing method to communicate packets among cores is proposed in this paper. To make efficient use of the MPSoC platform to carry out photon-mapping rendering, many methods concerning the increase of load balancing, the efficient use of memory, and the decrease of communication cost to achieve a scalable application are explored in this paper. The resulting MPSoC platform is verified and evaluated by cycle-accurate simulations for different sizes of the mesh NoC. As expected, the proposed methods can obtain excellent load balancing and achieve a maximum of 44.3 times faster on an 8-by-8 MPSoC platform than on a single-core MPSoC platform.

Performance modeling of [formula omitted]-dimensional mesh networks

Mesh-based interconnection networks are the most popular inter-processor communication infrastructures used in current parallel supercomputers. Although many analytical models of n -D torus interconnection networks have been reported in the literature over the last decade, few analytical models have been proposed for the 2-D mesh case (and not for the general n -D mesh network) using inaccurate approximations as they have not fully incorporated the asymmetry effects of the mesh topology, in order to reduce the model complexity. There has not been reported, to the best of our knowledge, a performance model that can deal with the n -D mesh network. To fill this gap, in this paper, we propose the first analytical performance model of the n -D mesh using adaptive wormhole routing. To this end, we calculate the exact traffic rates over different network channels and determine the average message latency by averaging over the message latency values corresponding to all possible source–destination pairs of nodes in the network. Simulation results show that the proposed model can predict the message latency fairly accurately under various working conditions.

Adaptive wormhole routing in tori with faults: A mathematical approach

Fault-tolerance in a communication network is defined as the ability of the network to effectively utilize its redundancy in the presence of faulty components (i.e., nodes or links). New technologies of integration now enable the design of computing systems with hundreds and even thousands of independent processing elements which can cooperate on the solution of the same problem for a corresponding improvement in the execution time. However, as the number of processing units increases, concerns for reliability and continued operation of the system in the presence of failures must be addressed. Adaptive routing algorithms have been frequently suggested as a means of improving communication performance in large-scale massively parallel computers, Multiprocessors System-on-Chip (MP-SoCs), and peer-to-peer communication networks. Before such schemes can be successfully incorporated in networks, it is necessary to have a clear understanding of the factors which affect their performance potential. This paper proposes a novel analytical model to investigate the performance of five prominent adaptive routings in wormhole-switched 2-D tori fortified with an effective scheme suggested by Chalasani and Boppana [S. Chalasani, R.V. Boppana, Adaptive wormhole routing in tori with faults, IEE Proc. Comput. Digit. Tech. 42(6) (1995) 386–394], as an instance of a fault-tolerant method widely used in the literature to achieve high adaptivity and support inter-processor communications in parallel computers. Analytical approximations of the model are confirmed by comparing them with those obtained through simulation experiments.

Effects of Adaptive Wormhole Routing in Event Builder Networks

The data acquisition system of the CMS experiment at the Large Hadron Collider features a two-stage event builder, which combines data from about 500 sources into full events at an aggregate throughput of 100 GB/s. To meet the requirements, several architectures and interconnect technologies have been quantitatively evaluated. Myrinet will be used for the communication from the underground frontend devices to the surface event building system. Gigabit Ethernet is deployed in the surface event building system. Nearly full bi-section throughput can be obtained using a custom software driver for Myrinet based on barrel shifter traffic shaping. This paper discusses the use of Myrinet dual-port network interface cards supporting channel bonding to achieve virtual 5 GBit/s links with adaptive routing to alleviate the throughput limitations associated with wormhole routing. Adaptive routing is not expected to be suitable for high-throughput event builder applications in high-energy physics. To corroborate this claim, results from the CMS event builder preseries installation at CERN are presented and the problems of wormhole routing networks are discussed.

Mathematical performance modelling of adaptive wormhole routing in optoelectronic hypercubes

In this paper, an analytical performance model for adaptive wormhole routing in the hypercube-based optical transpose interconnection system (OTIS-hypercube) is proposed and validated. Using this model, the performance merits of the OTIS-hypercube are discussed. We also compare the performance of the OTIS-hypercube with that of equivalent hypercube network under different implementation constraints. Compared to pure simulation results, the presented model can serve as a more appropriate and compact method to display the performance characteristics of OTIS-hypercube networks.

An accurate performance model of fully adaptive routing in wormhole-switched two-dimensional mesh multicomputers

Numerous analytical performance models have been proposed for deterministic wormhole-routed mesh networks while only a single model, to our best knowledge, has been suggested for fully adaptive wormhole routing in mesh interconnection networks. This paper proposes a new and accurate analytical performance model for fully adaptive wormhole-routed mesh networks. Simulation results show that unlike the previously proposed model which is only accurate in light traffic loads, this model can be used for the performance analysis of almost all traffic loads.

Adaptive Wormhole Routing in Mesh-Hypercube Network

Adaptive Wormhole Routing in Mesh-Hypercube Network

An analytical model of adaptive wormhole routing with time-out

Although many adaptive routing algorithms have been proposed for wormhole-routed networks, it is necessary to have clear understanding of the factors that affect their potential performance before they can be widely adopted in commercial multicomputers. This paper proposes a new analytical model of an adaptive routing algorithm proposed by Duato [Future Gener. Comp. Sys. 10 (10) (1994) 45]. The main feature of this routing algorithm is the use of a time-out mechanism to select a particular class of virtual channels at a given router. This has the advantage of reducing virtual channels multiplexing, leading to improvement in network performance. Simulation experiments reveal that the proposed analytical model predicts message latency with a good degree of accuracy.

Performance Tuning of Adaptive Wormhole Routing through Selection Function Choice

Many adaptive routing algorithms have been proposed for wormhole-routed interconnection networks. Comparatively little work, however, has been done on determining how the selection function (routing policy) affects the performance of an adaptive routing algorithm. In this paper, we present a detailed simulation study of various selection functions for fully adaptive wormhole routing on two-dimensional meshes. The simulation results show that the choice of selection function has a significant effect on the average message latency. In addition, it is possible to find a single selection function that exhibits excellent performance across a wide range of traffic patterns, network sizes, and number of virtual channels. Thus, a well-chosen selection function for an adaptive routing algorithm can lead to consistently better performance than an arbitrary selection function. One of the selection functions considered is a theoretically optimal selection function (IEEE Trans. Comput.38(10) (October 1989), 1362–1371). We show that although theoretically optimal, the actual performance of the optimal selection function is not always best. An explanation and interpretation of the results is provided.

A Performance Model of Adaptive Wormhole Routing in k -Ary n -Cubes in the Presence of Digit-Reversal Traffic

Several analytical models of fully adaptive routing in wormhole-routed k-ary n-cubes under the uniform traffic pattern have recently been proposed in the literature. Although the uniform reference model has been widely used by researchers, it is not always true in practice as there are many applications that exhibit traffic nonuniformity. There has hardly been any study that describes an analytical model of fully adaptive routing under nonuniform traffic conditions. This paper describes the first analytical model of fully adaptive routing in k-ary n-cubes in the presence of nonuniform traffic generated by the digit-reversal permutation, which is an important communication operation found in many matrix computation problems. Results obtained through simulation experiments confirm that the model predicts message latency with a good degree of accuracy under different working conditions.

On the merits of hypermeshes and tori with adaptive routing

Most existing multicomputers employ the torus topology along with deterministic routing to ensure simple router implementation, and thus fast communication. Efficient adaptive routing algorithms with minimum implementation requirements have recently been proposed to overcome the limitations of deterministic routing. Such algorithms have been incorporated in the latest generation of multicomputers, e.g. the Cray T3E, which are still based on low-dimensional k-ary n-cubes. Our previous studies have shown that a hypergraph network, referred to as the distributed crossbar switch hypermesh (DCSH), has several topological and performance advantages over traditional k-ary n-cubes when deterministic routing is used. This paper evaluates the relative merits of the DCSH and a variant of k-ary n-cubes, the torus, in the context of adaptive routing. The evaluation takes into account the effects of increased switching delays due to adaptivity, and implementation costs for various technologies (e.g. VLSI and multiple-chip technology). The results reveal that the DCSH is a potential alternative as a future high-performance multicomputer network, which can fully exploit the benefits of adaptive wormhole routing. Even though the torus has higher bandwidth channels than its DCSH counterpart, due to its simpler interconnect structure, adaptivity cannot reduce its higher message blocking delays inherent in its topology.

Performance analysis of adaptive wormhole routing in a two-dimensional torus

This paper presents an analytical evaluation of the performance of adaptive wormhole routing in a two-dimensional torus. Our analysis focuses on minimal and fully adaptive wormhole routing that allows a message to use any shortest path between source and destination. A validation of the analysis through simulation is presented to demonstrate the accuracy of the obtained results. Finally, we remark that no theoretical limitation prevents the extension of our analytical approach to the evaluation of the performance of adaptive wormhole routing in hypercubes or other symmetric topologies with wrap-around connections.

On the performance of adaptive wormhole routing in the bi-directional torus network: a hot spot analysis

Very few analytical models of multicomputer networks operating under non-uniform traffic have been reported in the literature. As a result, most existing studies have relied on simulation and measurement experiments to assess the performance of adaptive routing algorithms in wormhole-routed networks under such traffic conditions. This paper introduces an analytical model of adaptive routing in bi-directional tori in the presence of hot spots. Results from simulation experiments show close agreement with those predicted by the model.

An analytical model of adaptive wormhole routing in hypercubes in the presence of hot spot traffic

Analytical models of fully adaptive routing for common wormhole-routed networks (e.g., hypercubes) under the uniform traffic pattern have recently been reported in the literature. However, many studies have revealed that the performance advantages of adaptive routing over deterministic routing is more noticeable when the traffic is nonuniform due to, for example, the existence of hot spots in the network. This paper proposes a new queueing model of fully adaptive routing in the hypercube in the presence of hot spot traffic. The analysis focuses on Duato's algorithm, but can easily be applied to other fully adaptive routing algorithms. Results from simulation experiments are presented to validate the model.

An accurate analytical model of adaptive wormhole routing in k-ary n-cubes interconnection networks

Many fully adaptive algorithms have been proposed in the literature over the past decade. The performance characteristics of most of these algorithms have been analysed by means of software simulation only. This paper proposes an analytical model to predict message latency in wormhole-routed k-ary n-cubes with fully adaptive routing. The analysis focuses Duato’s fully adaptive routing algorithm [IEEE Trans. Parall. Distrib. Syst. 4 (2) (1993) 320], which is widely accepted as the most general algorithm for achieving adaptivity in wormhole-routed networks while allowing for an efficient router implementation. The proposed model is general in that it exhibits a good degree of accuracy for various network sizes and under different operating conditions.

AN ADAPTIVE FAULT-TOLERANT WORMHOLE ROUTING ALGORITHM FOR HYPERCUBES

In this paper, we present an adaptive fault-tolerant wormhole routing algorithm for hypercubes by using 4 virtual networks. Each node is identified to be in one of the four states: safe, ordinarily unsafe, strongly unsafe, and faulty. Based on the concept of unsafe nodes, we design a routing algorithm for hypercubes that can tolerate at least n-1 faulty nodes and can route a message via a path of length no more than the Hamming distance between the source and destination plus four. Previous algorithms which achieve the same fault tolerant ability need at least 5 virtual channels per physical channel. Simulation results show that our algorithm outperforms previous known results.

The odd-even turn model for adaptive routing

This paper presents a model for designing adaptive wormhole routing algorithms for meshes without virtual channels. The model restricts the locations where some turns can be taken so that deadlock is avoided. In comparison with previous methods, the degree of routing adaptiveness provided by the model is more even for different source-destination pairs. The mesh network may benefit from this feature in terms of communication efficiency. Simulation results show that the even adaptiveness provided by the odd-even turn model makes message routing less vulnerable to nonuniform factors such as hot spot traffic. In addition, this property results in a smaller fluctuation of the network performance with respect to different traffic patterns.

PATH SELECTION FOR REAL-TIME COMMUNICATION IN WORMHOLE NETWORKS

For real-time communication, we must be able to guarantee timely delivery of messages. In a previous paper, Kim et al. presented a real-time communication method for networks which uses a deterministic wormhole routing algorithm. It would be more desirable to be able to use an adaptive wormhole routing algorithm. However, the use of an adaptive algorithm results in highly unpredictable communication delays because the path used by each message cannot be known in advance. Thus, an alternative is to use a flexible wormhole routing algorithm, in which one of a set of predefined paths is chosen (in advance) for each pair of communicating nodes. With flexible routing, real-time communication guarantees are again possible while making more effective use of the available network resources than deterministic routing. This paper examines the problem of selecting a set of paths to maximize the probability of meeting real-time communication guarantees for a set of communicating nodes. Since this problem is NP-hard, a heuristic solution is proposed and compared with previous path selection algorithms. Simulation results are used to show that the proposed path selection algorithm outperforms all previous algorithms.