New Fault Tolerant Multicast Routing Techniques to Enhance Distributed-Memory Systems Performance

Distributed-memory systems are a key to achieve high performance computing and the most favorable architectures used in advanced research problems. Mesh connected multicomputer are one of the most popular architectures that have been implemented in many distributed-memory systems. These systems must support communication operations efficiently to achieve good performance. The wormhole switching technique has been widely used in design of distributed-memory systems in which the packet is divided into small flits. Also, the multicast communication has been widely used in distributed-memory systems which is one source node sends the same message to several destination nodes. Fault tolerance refers to the ability of the system to operate correctly in the presence of faults. Development of fault tolerant multicast routing algorithms in 2D mesh networks is an important issue. This dissertation presents, new fault tolerant multicast routing algorithms for distributed-memory systems performance using wormhole routed 2D mesh. These algorithms are described for fault tolerant routing in 2D mesh networks, but it can also be extended to other topologies. These algorithms are a combination of a unicast-based multicast algorithm and tree-based multicast algorithms. These algorithms works effectively for the most commonly encountered faults in mesh networks, f-rings, f-chains and concave fault regions. It is shown that the proposed routing algorithms are effective even in the presence of a large number of fault regions and large size of fault region. These algorithms are proved to be deadlock-free. Also, the problem of fault regions overlap is solved. Four essential performance metrics in mesh networks will be considered and calculated; also these algorithms are a limited-global-information-based multicasting which is a compromise of local-information-based approach and global-information-based approach. Data mining is used to validate the results and to enlarge the sample. The proposed new multicast routing techniques are used to enhance the performance of distributed-memory systems. Simulation results are presented to demonstrate the efficiency of the proposed algorithms

A Deadlock – Free Routing Algorithm for Torus Network

TORUS is a n-dimensional network topology. Each dimension will have k nodes.  A routing algorithm determines the sequence of channels for a packet to traverse from the source to destination. A new router design that significantly reduces the main drawback of worm hole switching – latency, is presented in this paper. Worm-hole switching is combined with virtual channel to provide better performance. Packet deadlock is avoided by verifying the freeness of the nodes before sending the packets to that node. The traditional ‘wormhole switching’ mechanism for routing in the torus network has the disadvantages such as link contention, message latency, need for large buffer size and finally a massive deadlock may appear. The recently proposed ‘clue’ algorithm, has the disadvantages such as difficulty in cut through the link by the packets, says nothing about loss of packets between a hop and storage overhead and complexity in dividing the virtual channels. We proposed an ‘Advanced Clue’ algorithm by combining the concepts of clue and flow controlled clue and also overcome the disadvantages of clue. We use two virtual channels and a buffer which gives a combination of clue and flow controlled clue. We also propose conditions that satisfy the reliability of the packet delivery between hops. The packet will be sent to the next hop and buffered in the current hop. The sending hop will set a timer and wait for the acknowledgement. If the acknowledgement is not arrived till the timer expired then, the packet will be resend, and otherwise the packet will be removed from the buffer. Keywords: Torus, Virtual channels, Cut – through Switching, Wormhole switching

The Effect Of Hot Spots On The Performance Of Mesh--Based Networks

Direct network performance is affected by different design parameters which include number of virtual channels, number of ports, routing algorithm, switching technique, deadlock handling technique, packet size, and buffer size. Another factor that affects network performance is the traffic pattern. In this thesis, we study the effect of hotspot traffic on system performance. Specifically, we study the effect of hotspot factor, hotspot number, and hot spot location on the performance of mesh-based networks. Simulations are run on two network topologies, both the mesh and torus. We pay more attention to meshes because they are widely used in commercial machines. Comparisons between oblivious wormhole switching and chaotic packet switching are reported. Overall packet switching proved to be more efficient in terms of throughput when compared to wormhole switching. In the case of uniform random traffic, it is shown that the differences between chaotic and oblivious routing are indistinguishable. Networks with low number of hotspots show better performance. As the number of hotspots increases network latency tends to increase. It is shown that when the hotspot factor increases, performance of packet switching is better than that of wormhole switching. It is also shown that the location of hotspots affects network performance particularly with the oblivious routers since their achieved latencies proved to be more vulnerable to changes in the hotspot location. It is also shown that the smaller the size of the network the earlier network saturation occurs. Further, it is shown that the chaos router’s adaptivity is useful in this case. Finally, for tori, performance is not greatly affected by hotspot presence. This is mostly due to the symmetric nature of tori

LAPSES: A Recipe for High-Performance Adaptive Router Design

Earlier research has shown that adaptive routing can help in improving network performance. However, it has not received adequate attention in commercial routers mainly due to the additional hardware complexity, and the perceived cost and performance degradation that may result from this complexity. These concerns can be mitigated if one can design a cost-effective router that can support adaptive routing. This paper proposes a three step recipe — Look-Ahead routing, intelligent Path Selection, and an Economic Storage implementation, called the LAPSES approach — for cost-effective high performance pipelined adaptive router design. The first step, look-ahead routing, reduces a pipeline stage in the router by making table lookup and arbitration concurrent. Next, three new traffic-sensitive path selection heuristics (LRU, LFU and MAX-CREDIT) are proposed to select one of the available alternate paths. Finally, two techniques for reducing routing table size of the adaptive router are presented. These are called meta-table routing and economical storage. The proposed economical storage needs a routing table with only 9 and 27 entries for two and three dimensional meshes, respectively. All these design ideas are evaluated on a (16 16) mesh network via simulation. A fully adaptive algorithm and various traffic patterns are used to examine the performance benefits. Performance results show that the look-ahead design as well as the path selection heuristics boost network performance, while the economical storage approach turns out to be an ideal choice in comparison to full-table and meta-table options. We believe the router resulting from these three design enhancements can make adaptive routing a viable choice for interconnects.

More Improvement by Helping Ant to Fault-Tolerant Heuristic Routing Algorithm in Mesh Networks

Abstract: Routing with fault-tolerant mechanisms has a crucial effect on the fast exchange of information in variety of networks including mesh networks. This study attempts to choose an optimal path in terms of fault tolerance to transmit messages from source to destination while taking into account faulty nodes in such mesh networks. In this study, we take advantage of ant colony optimization algorithm to propose Adaptive Heuristic Routing algorithms to this problem. We use color pheromone ants to overcome problem of fail-recover behavior of network components. The proposed method is compared with fault-tolerant routing algorithm in mesh networks using the balanced ring. Simulation results depict that this method reacted quickly in terms of network faults, meanwhile in each time step the data can choose the optimal path to reach their destination. In this study, we improve performance of the proposed method using update ants to inform other nodes about the discovered shortest path. Simulation results show that the proposed method dramaticcaly increase efficiency of routing mechanism in mesh networks

Efficient mechanisms to provide fault tolerance in interconnection networks for pc clusters

Actualmente, los clusters de PC son un alternativa rentable a los computadores paralelos. En estos sistemas, miles de componentes (procesadores y/o discos duros) se conectan a través de redes de interconexión de altas prestaciones. Entre las tecnologías de red actualmente disponibles para construir clusters, InfiniBand (IBA) ha emergido como un nuevo estándar de interconexión para clusters. De hecho, ha sido adoptado por muchos de los sistemas más potentes construidos actualmente (lista top500). A medida que el número de nodos aumenta en estos sistemas, la red de interconexión también crece. Junto con el aumento del número de componentes la probabilidad de averías aumenta dramáticamente, y así, la tolerancia a fallos en el sistema en general, y de la red de interconexión en particular, se convierte en una necesidad. Desafortunadamente, la mayor parte de las estrategias de encaminamiento tolerantes a fallos propuestas para los computadores masivamente paralelos no pueden ser aplicadas porque el encaminamiento y las transiciones de canal virtual son deterministas en IBA, lo que impide que los paquetes eviten los fallos. Por lo tanto, son necesarias nuevas estrategias para tolerar fallos. Por ello, esta tesis se centra en proporcionar los niveles adecuados de tolerancia a fallos a los clusters de PC, y en particular a las redes IBA. En esta tesis proponemos y evaluamos varios mecanismos adecuados para las redes de interconexión para clusters. El primer mecanismo para proporcionar tolerancia a fallos en IBA (al que nos referimos como encaminamiento tolerante a fallos basado en transiciones; TFTR) consiste en usar varias rutas disjuntas entre cada par de nodos origen-destino y seleccionar la ruta apropiada en el nodo fuente usando el mecanismo APM proporcionado por IBA. Consiste en migrar las rutas afectadas por el fallo a las rutas alternativas sin fallos. Sin embargo, con este fin, es necesario un algoritmo eficiente de encaminamiento capaz de proporcionar suficientesMontañana Aliaga, JM. (2008). Efficient mechanisms to provide fault tolerance in interconnection networks for pc clusters [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/2603Palanci

Topology Agnostic Methods for Routing, Reconfiguration and Virtualization of Interconnection Networks

Modern computing systems, such as supercomputers, data centers and multicore chips, generally require efficient communication between their different system units; tolerance towards component faults; flexibility to expand or merge; and a high utilization of their resources. Interconnection networks are used in a variety of such computing systems in order to enable communication between their diverse system units. Investigation and proposal of new or improved solutions to topology agnostic routing and reconfiguration of interconnection networks are main objectives of this thesis. In addition, topology agnostic routing and reconfiguration algorithms are utilized in the development of new and flexible approaches to processor allocation. The thesis aims to present versatile solutions that can be used for the interconnection networks of a number of different computing systems. No particular routing algorithm was specified for an interconnection network technology which is now incorporated in Dolphin Express. The thesis states a set of criteria for a suitable routing algorithm, evaluates a number of existing routing algorithms, and recommend that one of the algorithms – which fulfils all of the criteria – is used. Further investigations demonstrate how this routing algorithm inherently supports fault-tolerance, and how it can be optimized for some network topologies. These considerations are also relevant for the InfiniBand interconnection network technology. Reconfiguration of interconnection networks (change of routing function) is a deadlock prone process. Some existing reconfiguration strategies include deadlock avoidance mechanisms that significantly reduce the network service offered to running applications. The thesis expands the area of application for one of the most versatile and efficient reconfiguration algorithms available in the literature, and proposes an optimization of this algorithm that improves the network service offered to running applications. Moreover, a new reconfiguration algorithm is presented that supports a replacement of the routing function without causing performance penalties. Processor allocation strategies that guarantee traffic-containment commonly pose strict requirements on the shape of partitions, and thus achieve only a limited utilization of a system’s computing resources. The thesis introduces two new approaches that are more flexible. Both approaches utilize the properties of a topology agnostic routing algorithm in order to enforce traffic-containment within arbitrarily shaped partitions. Consequently, a high resource utilization as well as isolation of traffic between different partitions is achieved

Routing on the Channel Dependency Graph:: A New Approach to Deadlock-Free, Destination-Based, High-Performance Routing for Lossless Interconnection Networks

In the pursuit for ever-increasing compute power, and with Moore's law slowly coming to an end, high-performance computing started to scale-out to larger systems. Alongside the increasing system size, the interconnection network is growing to accommodate and connect tens of thousands of compute nodes. These networks have a large influence on total cost, application performance, energy consumption, and overall system efficiency of the supercomputer. Unfortunately, state-of-the-art routing algorithms, which define the packet paths through the network, do not utilize this important resource efficiently. Topology-aware routing algorithms become increasingly inapplicable, due to irregular topologies, which either are irregular by design, or most often a result of hardware failures. Exchanging faulty network components potentially requires whole system downtime further increasing the cost of the failure. This management approach becomes more and more impractical due to the scale of today's networks and the accompanying steady decrease of the mean time between failures. Alternative methods of operating and maintaining these high-performance interconnects, both in terms of hardware- and software-management, are necessary to mitigate negative effects experienced by scientific applications executed on the supercomputer. However, existing topology-agnostic routing algorithms either suffer from poor load balancing or are not bounded in the number of virtual channels needed to resolve deadlocks in the routing tables. Using the fail-in-place strategy, a well-established method for storage systems to repair only critical component failures, is a feasible solution for current and future HPC interconnects as well as other large-scale installations such as data center networks. Although, an appropriate combination of topology and routing algorithm is required to minimize the throughput degradation for the entire system. This thesis contributes a network simulation toolchain to facilitate the process of finding a suitable combination, either during system design or while it is in operation. On top of this foundation, a key contribution is a novel scheduling-aware routing, which reduces fault-induced throughput degradation while improving overall network utilization. The scheduling-aware routing performs frequent property preserving routing updates to optimize the path balancing for simultaneously running batch jobs. The increased deployment of lossless interconnection networks, in conjunction with fail-in-place modes of operation and topology-agnostic, scheduling-aware routing algorithms, necessitates new solutions to solve the routing-deadlock problem. Therefore, this thesis further advances the state-of-the-art by introducing a novel concept of routing on the channel dependency graph, which allows the design of an universally applicable destination-based routing capable of optimizing the path balancing without exceeding a given number of virtual channels, which are a common hardware limitation. This disruptive innovation enables implicit deadlock-avoidance during path calculation, instead of solving both problems separately as all previous solutions