REAL-TIME VIRTUAL CHANNEL FLOW-CONTROL

Real-time communication system support for large scale parallel multic omputers becomes an important issue as the number of real-time applica tions developed on these systems increases. Flow control is a key comp onent that affects the performance of the communication subsystem. We develop a range of new real-time virtual channel flow control schemes for wormhole networks. The flow control schemes differ in their priori ty mapping strategies, priority adjustment methods, and arbitration fu nctions. The priority mapping strategy and priority adjustment method of a how control scheme determine the priority of a message. The prior ity of a message is used for the virtual channel assignment and the ph ysical channel arbitration. We discuss the trade-off between the perfo rmance and the hardware cost of each flow control scheme. A simulator is implemented for studying the performance of the schemes, and simula tion experiments are designed to compare the importance of priority ma pping, priority adjustment and arbitration toward the system performan ce. As wormhole networks scale to larger sizes, the average distance b etween source and destination nodes increases. The flits of messages i n wormhole networks, which are buffered in nodes along the path from t he source to the destination, consume network resources in these nodes . Therefore, increased scaling may lead to increased resource consumpt ion, congestion, and late messages. In real-time systems, messages los e their value when they miss their deadlines. In order to reduce conge stion, we provide a scheme for dropping messages that miss their deadl ines. (C) 1996 Academic Press, Inc.