Jose Flich

A routing methodology for achieving fault tolerance in direct networks

Massively parallel computing systems are being built with thousands of nodes. The interconnection network plays a key role for the performance of such systems. However, the high number of components significantly increases the probability of failure. Additionally, failures in the interconnection network may isolate a large fraction of the machine. It is therefore critical to provide an efficient fault-tolerant mechanism to keep the system running, even in the presence of faults. This paper presents a new fault-tolerant routing methodology that does not degrade performance in the absence of faults and tolerates a reasonably large number of faults without disabling any healthy node. In order to avoid faults, for some source-destination pairs, packets are first sent to an intermediate node and then from this node to the destination node. Fully adaptive routing is used along both subpaths. The methodology assumes a static fault model and the use of a checkpoint/restart mechanism. However, there are scenarios where the faults cannot be avoided solely by using an intermediate node. Thus, we also provide some extensions to the methodology. Specifically, we propose disabling adaptive routing and/or using misrouting on a per-packet basis. We also propose the use of more than one intermediate node for some paths. The proposed fault-tolerant routing methodology is extensively evaluated in terms of fault tolerance, complexity, and performance.

NOCS '11 Proceedings of the Fifth ACM/IEEE International Symposium on Networks-on-Chip

In application-specific SoCs, the irregularity of the topology ends up in a complex implementation of the routing algorithm, usually relying on routing tables implemented with memory structures. As system size increases, the routing table increases in size with non-negligible impact on power, area and latency overheads. In this paper we present a routing implementation for application-specific SoCs able to implement in an efficient manner (without requiring routing tables and using a small logic block in every switch) a routing algorithm in these irregular networks. The mechanism relies on a tool that maps the initial irregular topology of the SoC system into a logical regular structure where the mechanism can be applied. We provide details on the mapping tool as well the proposed routing mechanism. Evaluation results show the effectiveness of the mapping tool as well as the low area and timing requirements of the mechanism. With the mapping tool and the routing mechanism complex irregular SoC topologies can now be supported without the use of routing tables.