A Comparative Study of Deadlock Recovery Schemes in Wormhole Routed Networks Jameel Ahmad Department of Computer Science & Engineering Integral University Lucknow, India Dr. Mohammadi Akheela Khanum Department of Computer Science & Engineering Integral University Lucknow, India Professor A. A. Zilli Department of Computer Science & Engineering Lucknow University Lucknow, India Abstract— Issue of deadlocks is a serious problem in wormhole routed networks. A number of deadlock handling algorithms have been proposed in literature. Some are based on deadlock prevention and avoidance and some on deadlock recovery. Since the deadlocks are rare events, only few resources should be dedicated to deal with these rare events [1]. So if a routing algorithm allows the network fully adaptively to form cycles then a deadlock recovery mechanism must be in place to resolve these deadlock cycles. Cost and performance is a major issue of concern in these algorithms. This paper presents a comparative study of three deadlock recovery schemes. Keywords—Wormhole routing, Deadlocks, Recovery, Avoidance, Parallel Computers. INTRODUCTION The parallel computers on large scientific and commercial scale are preferred candidates for facilitating high power computation characteristics. These computers system are arranged as an ensemble of the processing nodes and connected as well having their own resources like memory, processors, and other peripheral devices. These nodes are inter-connected with different topologies categorized as direct and indirect topology [4]. Massively parallel computers are important category of parallel machines that provide an envisioned computing platform for solving the challenging problems. Different variations of the machines are available commercially today. These machines are assembly of many nodes which can communicate each other with a set of switches and links of communication are collectively known by the interconnection network [12]. The performance of these inter-connection networks is very critical factor that affects the performance of these parallel machines. Wormhole switching is one of the most promising switching technique which has is applied to these inter- connection networks of the parallel multi-computers. The Wormhole switching technique is well suited for the applications in multi-computer inter-connection networks as it allows the design of simple and low cost hardware and router nodes, while provides low latency and high bandwidth communication [6]. The routing algorithms to route the packets in the wormhole networks are characterized by their approach and how they overcome the issue of deadlocks [7,8]. Earlier proposed work in literature has applied the view that the routing algorithm should be deadlock free. By applying sufficient condition to prevent the deadlock occurrence and by implementing a routing algorithm applying this condition during routing, freedom from deadlocks is guaranteed. These algorithms are known as deadlock avoidance algorithms for routing [4,15]. On the other hand a deadlock recovery algorithm allows the packets to route on all the available channels resource without restricting the possibility of deadlocks. If deadlocks occur, deadlock detection mechanism works and any particular deadlock recovery algorithm is invoked to break the deadlock cycles [5,11]. Both the techniques are almost similar by the fact that in every case the routing algorithm for resolution utilizes some resources, but the amount and cost of these resources differs. The fact has been established in research that deadlock situations are rare events in general. Due to this effect almost all the deadlock avoidance algorithms use expensive resources more than minimum required to avoid the deadlocks. This observation promotes the deadlock recovery techniques to implement more widely than deadlock avoidance techniques. The routing algorithms are characterized also by the extent of adaptivity they provide. The Deterministic Algorithms: The deterministic algorithms in the network do not have any adaptivity. The path for routing is determined by the source node, considering the source node and destination node only. The deterministic routers are fast and simple in design. They suffer serious deadlock situations and do not react to the current state of the network condition [12,15]. The Adaptive Algorithms: The Adaptive algorithms of routing on the other hand react to the network conditions and they allow the packets to route along the alternate paths. The routing decisions are taken by each intermediate node, along the path in a distributed manner [13]. International Journal of Engineering Research & Technology (IJERT) ISSN: 2278-0181 http://www.ijert.org IJERTV7IS070046 (This work is licensed under a Creative Commons Attribution 4.0 International License.) Published by : www.ijert.org Vol. 7 Issue 07, July-2018 87