High-performance routing in networks of workstations with irregular topology

Abstract

ÐNetworks of workstations are rapidly emerging as a cost-effective alternative to parallel computers. Switch-based interconnects with irregular topology allow the wiring flexibility, scalability, and incremental expansion capability required in this environment. However, the irregularity also makes routing and deadlock avoidance on such systems quite complicated. In current proposals, many messages are routed following nonminimal paths, increasing latency and wasting resources. In this paper, we propose two general methodologies for the design of adaptive routing algorithms for networks with irregular topology. Routing algorithms designed according to these methodologies allow messages to follow minimal paths in most cases, reducing message latency and increasing network throughput. As an example of application, we propose two adaptive routing algorithms for AN1 (previously known as Autonet). They can be implemented either by duplicating physical channels or by splitting each physical channel into two virtual channels. In the former case, the implementation does not require a new switch design. It only requires changing the routing tables and adding links in parallel with existing ones, taking advantage of spare switch ports. In the latter case, a new switch design is required, but the network topology is not changed. Evaluation results for several different topologies and message distributions show that the new routing algorithms are able to increase throughput for random traffic by a factor of up to 4 with respect to the original up à /down à algorithm, also reducing latency significantly. For other message distributions, throughput is increased more than seven times. We also show that most of the improvement comes from the use of minimal routing.

Descending layers routing: a deadlock-free deterministic routing using virtual channels in system area networks with irregular topologies

“…It adopts up*/down* routing to make acyclic virtual networks (layers). On the other hand, an adaptive escape-path routing proposed by Silla and Duato doesn't always guarantee minimal paths, however, it guarantees deadlock-free routing while still allowing cycles [18]. Since each packet in channels out of escape path is forwarded along a minimal path, most of packets take minimal paths in the Silla's routing.…”

“…To address these problems, improved routing methods, most of which make the use of additional virtual channels or buffers, have been recently proposed [18] [19] [9] [7] [13]. In the background of appearing such routing strategies, switching fabrics in recent SANs [20] [5] [17] have a sufficient amount of hardware for a limited number of virtual channels [3] or extra buffers for packets.…”

Deadlock-Free Fully Adaptive Routing in Irregular Networks without Virtual Channels

“…A general methodology for the design of adaptive routing algorithms for networks with irregular topology has been proposed in [26] by extending the Duato's protocol to the irregular networks. Puente, et al in [21] proposed a pseudoHamiltonian-cycle-based adaptive routing mechanism for irregular NOWs, which leads to apparent improvement over the classical up*/down* routing algorithm, which comes at an acceptable extra cost.…”

Deadlock-free routing based on ordered links

“…Subsequently, [10] describes a technique that uses alternative routes and relies on one subset of the alternatives (for each source and destination) to be deadlock-free to guarantee the routing function to be deadlock-free. This technique can be used to optimize the performance of known deadlock-free routes.…”

“…For each of the protocols (OPT, UD and BFOT) we used the hill-climbing algorithm to minimize the standard deviations 10 . Protocol OPT is consistently better then UD and BFOT.…”