Non-minimal Routing Research Articles

VCS: A method of in-order packet delivery for adaptive NoC routing

Adaptive routing proves its efficiency in sustaining higher network performance bypassing packets through alternate congestion-free minimal or non-minimal routes for a many-core on-chip communication system. It prevents the network from reaching an early saturation due to the stalling of packets in the priority-fixed shortest route for a longer period. However, routing packets adaptively to an alternate route instead of choosing the priority-fixed and shortest route may lead to an unintended state of delivering packets out-of-order sequence at the destination node that is not accepted by many message-passing systems. This ordering mismatch is due to allowing multiple alternate routes for packets of the same communication flow in adaptive mode. In such a case, a packet with a higher sequence number takes over another packet of the same communication flow having a lower sequence number. Storing and reordering all unordered packets of the same communication flow at the sink side becomes costlier due to the increasing area and power requirement. Ideally, the added memory size reaches to infinity for storing all unordered packets that belong to the same communication flow. In the proposed method, we guarantee delivery of all packets belongs to the same communication flow in an orderly manner under adaptive routing mode. In particular, we have proposed a flow-control policy based on a virtual circuit switch (VCS) method that exclusively won and reserve a virtual path for routing packets in an adaptive mode for each communication flow. To maximize network performance, we allow sharing of the reserved path among packets of different communication flows, routing under priority fix deterministic mode. The method saves need of having additional memory unit for storing all unordered packets while guaranteeing the packet’s ordering sequence at the destination end. An experiment conducted on two different size Mesh networks (8x8 and 12x12) under several synthetic traffic and benchmark application reveals that our virtual circuit switching (VCS) based proposed method offers a significant improvement over the state-of-the-art packet reordering method (ROR) and two similar type of research works. Our simulation based experimental result shows that method offers a 60% higher saturation point and 21% improvements (maximum) in throughput while offering a reduction of 60% in NoC area and 58% power value compared to the baseline reorder (ROR) method.

Scalable Design Methodology and Online Algorithm for TSV-Cluster Defects Recovery in Highly Reliable 3D-NoC Systems

3D-Network-on-Chips exploit the benefits of Network-on-Chips and 3D-Integrated Circuits allowing them to be considered as one of the most advanced and auspicious communication methodologies. On the other hand, the reliability of 3D-NoCs, due to the vulnerability of Through Silicon Vias, remains a major problem. Most of the existing techniques rely on correcting the TSV defects by using redundancies or employing routing algorithms. Nevertheless, they are not suitable for TSV-cluster defects as they can either lead to costly area and power consumption overheads, or they may result in non-minimal routing paths; thus, posing serious threats to the system reliability and overall performance. In this work, we present a scalable and low-overhead TSV usage and design method for 3D-NoC systems where the TSVs of a router can be utilized by its neighbors to deal with the cluster open defects. An adaptive online algorithm is also introduced to assist the proposed system to immediately work around the newly detected defects without using redundancies. The experimental results show the proposal ensure less than 2 percent of the routers being disabled, even with 50 percent of the TSV clusters defects. The performance evaluations also demonstrate unchanged performances for real applications under 5 percent of cluster defects.

A Non-Minimal Routing Algorithm for Aging Mitigation in 2D-Mesh NoCs

Due to technology scaling, aging issue is becoming one of major concerns in the design of network-on-chip (NoC). The imbalanced workload distribution and routing algorithm cause aging hotspots , where a certain group of routers have higher aging effect than others. This can possibly lead to shorter lifetime of NoC. Most existing aging-aware routing algorithms are based on minimal routing, which suffers from less degree of adaptiveness compared to non-minimal routing. Thus, they are inefficient to mitigate the aging effect of routers. In this paper, we propose to use a non-minimal routing scheme to detour the traffic away from the aging hotspots , with the objective of mitigating the aging effect for NoCs. The problem is formulated as a bottleneck shortest path problem and solved using a dynamic programming approach. Finally, the experimental results show that compared to the state-of-the-art aging-aware routing algorithm, the non-minimal routing algorithm has up to 20% lifetime improvement for hotspot traffic patterns and realistic workload traces.

ACOR: Adaptive congestion-oblivious routing in dragonfly networks

Low-diameter network topologies require non-minimal routing to avoid network congestion, such as Valiant routing. This increases base latency but avoids congestion issues. Optimized restricted variants focus on reducing path length. However, these optimizations only reduce paths for local traffic, where source and destination of each packet belong to the same partition of the network. This paper introduces ACOR: Adaptive Congestion-Oblivious Routing. ACOR leverages the restricted and recomputation mechanisms to reduce path length for local and global traffic, and extends it when the network conditions are adverse. ACOR relies on a sequence of misrouting policies ordered by path length. A hysteresis mechanism improves performance and avoids variability in the results. The ACOR mechanism can be combined with other non-minimal routing mechanism such as Piggyback. Results show that ACOR improves base latency in all cases, up to 28% standalone and up to 25.5% when combined with Piggyback, while requiring a simple implementation.

Non-minimal, turn-model based NoC routing

In this study, it is shown that any deadlock-free, turn-model based minimal routing algorithm can be extended to a non-minimal routing algorithm. Specifically, three novel non-minimal NoC routing algorithms are proposed based on the Odd–Even, West-First, and Negative-First turn models, respectively. These algorithms are not only deadlock free and livelock free, but can also leverage non-minimal routing paths to avoid traffic congestion and improve fault tolerance. Moreover, these algorithms are backward compatible with existing minimal routing schemes. As a result, they represent an ideal routing solution to NoC-based interconnections designed for both existing and emerging embedded multicore systems.

Flattened butterfly

Increasing integrated-circuit pin bandwidth has motivateda corresponding increase in the degree or radix of interconnection networksand their routers. This paper introduces the flattened butterfly, a cost-efficient topology for high-radix networks. On benign (load-balanced) traffic, the flattened butterfly approaches the cost/performance of a butterfly network and has roughly half the cost of a comparable performance Clos network.The advantage over the Clos is achieved by eliminating redundant hopswhen they are not needed for load balance. On adversarial traffic, the flattened butterfly matches the cost/performance of a folded-Clos network and provides an order of magnitude better performance than a conventional butterfly.In this case, global adaptive routing is used to switchthe flattened butterfly from minimal to non-minimal routing - usingredundant hops only when they are needed. Minimal and non-minimal, oblivious and adaptive routing algorithms are evaluated on the flattened butterfly.We show that load-balancing adversarial traffic requires non-minimalglobally-adaptive routing and show that sequential allocators are required to avoid transient load imbalance when using adaptive routing algorithms.We also compare the cost of the flattened butterfly to folded-Clos, hypercube,and butterfly networks with identical capacityand show that the flattened butterfly is more cost-efficient thanfolded-Clos and hypercube topologies.

Flattened Butterfly Topology for On-Chip Networks

With the trend towards increasing number of cores in a multicore processors, the on-chip network that connects the cores needs to scale efficiently. In this work, we propose the use of high-radix networks in on-chip networks and describe how the flattened butterfly topology can be mapped to on-chip networks. By using high-radix routers to reduce the diameter of the network, the flattened butterfly offers lower latency and energy consumption than conventional on-chip topologies. In addition, by properly using bypass channels in the flattened butterfly network, non-minimal routing can be employed without increasing latency or the energy consumption.

A Generic Design Methodology for Deadlock-Free Routing in Multicomputer Networks

This paper introduces a generic methodology for defining deadlock-free wormhole routing schemes in any arbitrary network. The basic strategy is to partition a graph into subdigraphs with no cyclic dependencies and selectively assign virtual channels. The usefulness of our scheme is shown for the n-dimensional hypercube, the n-dimensional mesh, and the k-ary n-cube torus by identifying subdigraph characteristics that ensure acyclic routing. Further generalization which allows partial cyclic dependencies without deadlock is achieved by our extended generic methodology. We also illustrate how to identify shortest fixed path and nonminimal adaptive routing schemes using minimum required channels.

Unicast-based multicast algorithm in wormhole-routed star graph interconnection networks

A contention-free unicast-based multicast algorithm is developed for wormhole-routed star graph interconnection networks. Since the size of the buffers in the wormhole routing controller is much smaller than the size of the message, only destination nodes of multicast should receive message and store it in their local buffers; all other nodes can only relay message via their routing controllers. For this reason, the neighbor-to-neighbor communications approach (used for developing broadcast, scatter and total exchange algorithms) is replaced with a hierarchical approach: a multicast tree composed of unicasts, in which only destination nodes receive the message. Furthermore, a methodology for proving the contention-free property of the hierarchical multicast implementation of the algorithm is developed. This methodology provides sufficient conditions for contention avoidance in the multicast algorithm regardless of the number of simultaneous unicasts permitted by the hardware architecture of the communication processor from the particular node. In order to eliminate contention in the multicast algorithm, a deterministic nonminimal routing algorithm is developed as well. It is shown that the proposed nonminimal routing uses only the same number of virtual channels, ( n−1) required by the minimal routing to avoid deadlock. This feature allows minimal and nonminimal routing to exist in the network at the same time.

A necessary and sufficient condition for deadlock-free routing in cut-through and store-and-forward networks

This paper develops the theoretical background for the design of deadlock-free adaptive routing algorithms for virtual cut-through and store-and-forward switching. This theory is valid for networks using either central buffers or edge buffers. Some basic definitions and three theorems are proposed, developing conditions to verify that an adaptive algorithm is deadlock-free, even when there are cyclic dependencies between routing resources. Moreover, we propose a necessary and sufficient condition for deadlock-free routing. Also, a design methodology is proposed. It supplies fully adaptive, minimal and non-minimal routing algorithms, guaranteeing that they are deadlock-free. The theory proposed in this paper extends the necessary and sufficient condition for wormhole switching previously proposed by us. The resulting routing algorithms are more flexible than the ones for wormhole switching. Also, the design methodology is much easier to apply because it automatically supplies deadlock-free routing algorithms.

Adaptive Multicast Wormhole Routing in 2D Mesh Multicomputers

The issues of adaptive multicast wormhole routing in 2D mesh multicomputers are studied. Three adaptive multicast wormhole routing strategies are proposed and evaluated. The methods include minimal partially adaptive, minimal fully adaptive, and nonminimal adaptive routing. All the algorithms are shown to be deadlock-free. A study has been conducted that compares the performance of these multicast algorithms. The results show that the minimal fully adaptive routing method creates the least traffic; however, double vertical channels are required in order to avoid deadlock. The nonminimal routing algorithm exhibits the best adaptivity, although it creates more network traffic than the other methods.

Valved routing: efficient flow control for adaptive nonminimal routing in interconnection networks

Adaptive nonminimal routing (or misrouting) may move messages away from their destinations to temporarily cope with the dynamic load in an interconnection network. In most cases, misrouting is more powerful and flexible than minimal routing, especially under nonuniform load distribution. However, to take advantage of its misrouting, we have to avoid deadlock, livelock, and starvation in the network and to maintain the network performance across all levels of loading. In this paper, we propose a new flow control scheme for misrouting, called valved routing. Valved routing controls message injection and transmission through logical valves associated with the router ports. Designing routers using valved routing requires a proper choice of design parameters. We will discuss how to find the range of feasible design parameters. Issues in implementing routers using valved routing will also be addressed. We have conducted extensive simulations to compare the performance of routers with and without valved routing. Our simulation results show that valved routing has promising performance advantages, at light as well as heavy network load. Compared with the voluntary misrouting, valved routing performs better in network throughput without sacrificing the latency. >