RESYNCHRONIZATION OF MULTIPROCESSOR SCHEDULES: PART 1 -- FUNDAMENTAL CONCEPTS AND UNBOUNDED-LATENCY ANALYSIS

This paper introduces a technique, called resynchronization, for reducing synchronization overhead in embedded multiprocessor implementations. The technique exploits the well-known observation [35] that in a given multiprocessor implementation, certain synchronization operations may be redundant in the sense that their associated sequencing requirements are ensured by other synchronizations in the system. The goal of resynchronization is to introduce new synchronizations in such a way that the number of additional synchronizations that become redundant exceeds the number of new synchronizations that are added, and thus the net synchronization cost is reduced. Our study is based in the context of self-timed execution of iterative dataflow programs. An iterative dataflow program consists of a dataflow representation of the body of a loop that is to be iterated infinitely; dataflow programming in this form has been employed extensively, particularly in the context of software for digital signal processing applications. Self-timed execution refers to a combined compile-time/run-time scheduling strategy in which processors synchronize with one another only based on inter-processor communication requirements, and thus, synchronization of processors at the end of each loop iteration does not generally occur. After reviewing our model for the analysis of synchronization overhead, we define the general form of our resynchronization problem; we show that optimal resynchronization is intractable by establishing a correspondence to the set covering problem; and based on this correspondence, we develop an efficient heuristic for resynchronization. Also, we show that for a broad class of iterative dataflow graphs, optimal resynchronizations can be computed by means of an efficient polynomial-time algorithm. We demonstrate the utility of our resynchronization techniques through a practical example of a music synthesis system