Sundararajan Sriram

Minimizing synchronization overhead in statically scheduled multiprocessor systems

Synchronization overhead can significantly degrade performance in embedded multiprocessor systems. This paper develops techniques to determine a minimal set of processor synchronizations that are essential for correct execution in an embedded multiprocessor implementation. Our study is based in the context of self-timed execution of iterative dataflow programs; dataflow programming in this form has been applied extensively, particularly in the context of signal processing software. 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. We introduce a new graph-theoretic framework, based on a data structure called the synchronization graph, for analyzing and optimizing synchronization overhead in self-timed, iterative dataflow programs. We also present an optimization that involves converting a synchronization graph that is not strongly connected into a strongly connected graph.

Resynchronization for multiprocessor DSP systems

This paper introduces a technique, called resynchronization, for reducing synchronization overhead in multiprocessor implementations of digital signal processing (DSP) systems. The technique applies to arbitrary collections of dedicated, programmable or configurable processors, such as combinations of programmable DSPs, ASICs, and FPGA subsystems. Thus, it is particularly well-suited to the evolving trend toward heterogeneous single-chip multiprocessors in DSP systems. Resynchronization exploits the well-known observation 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 original 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 on the context of self-timed execution for iterative dataflow specifications of DSP applications. An iterative dataflow specification consists of a dataflow representation of the body of a loop that is to be iterated indefinitely; dataflow programming in this form has been employed extensively in the DSP domain.

Latency-constrained resynchronization for multiprocessor DSP implementation

Resynchronization is a post-optimization for static multiprocessor schedules in which extraneous synchronization operations are introduced in such a way that the number of original synchronizations that consequently become redundant significantly exceeds the number of additional synchronizations. Redundant synchronizations are synchronization operations whose corresponding sequencing requirements are enforced completely by other synchronizations in the system. The amount of run-time overhead required for synchronization can be reduced significantly by eliminating redundant synchronizations. However, since additional serialization is imposed by the new synchronizations resynchronization can produce significant increase in latency. This paper addresses the problem of computing an optimal resynchronization (one that results in the lowest average rate at which synchronization operations have to be performed) among all resynchronizations that do not increase the latency beyond a prespecified upper bound L/sub max/. Our study is based on the context of self-timed execution of iterative data flow programs, which is an implementation model that has been applied extensively for digital signal processing systems.

Self-timed resynchronization: a post-optimization for static multiprocessor schedules

In a shared-memory multiprocessor system, it is possible that certain synchronization operations are redundant that is, their corresponding sequencing requirements are enforced completely by other synchronizations in the system-and can be eliminated without compromising correctness. This paper addresses the problem of adding new synchronization operations in a multiprocessor implementation in such a way that the number of original synchronizations that consequently become redundant significantly exceeds the number of new synchronizations. We refer to this approach to reducing synchronization overhead as resynchronization. We formally define the resynchronization problem, we show that optimal resynchronization is NP-hard, and we propose a family of heuristics for this problem. Finally we present a practical example where resynchronization is useful.