Software-Based Deadlock Recovery Technique for True Fully Adaptive Routing in Wormhole Networks

Networks using wormhole switching have traditionally relied upon deadlock avoidance strategies for the design of deadlock-free routing algorithms. More recently, deadlock recovery strategies have begun to gain acceptance. In particular, progressive deadlock recovery techniques are very attractive because they allocate a few dedicated resources to quickly deliver deadlocked packets, instead of killing them. Deadlock recovery is based on the assumption that deadlocks are rare. Very recently, the frequency of deadlock occurrence was measured [21, 18], showing that deadlocks are highly unlikely when enough routing freedom is provided. However, deadlocks are more prone when the network is close to or beyond saturation. Additionally, some performance degradationhas been observed at saturation. Similar performance degradation behavior at saturation was also observed in networks using deadlock avoidance strategies [9]. In this paper we take a different approach to handle deadlocks and performance degradation. We propose the use of an injection limitation mechanism that prevents performance degradation near the saturation point and reduces the probability of deadlock to negligible values even when fully adaptive routing is used. We also propose an improved deadlock detection mechanism that only uses local information, detects all the deadlocks, and considerably reduces the probability of false deadlock detection over previous proposals. In the rare case when impending deadlock is detected, our proposed recovery technique absorbs the deadlocked message at the current node and later re-injects it for continued routing towards its destination. Performance evaluation results show that our new approach to deadlock handling is more efficient than previously proposed techniques.