Utilization Improvement by Enforcing Mutual Exclusive Task Execution in Modal Stream Processing Applications

Abstract

Real-time dataflow analysis techniques for multiprocessor systems ignore that the execution of tasks belonging to different operation modes are mutually exclusive. This results in more resources being reserved than strictly needed and a low resource utilization. In this paper we present a dataflow analysis approach which takes into account that tasks belonging to different modes often execute mutually exclusive. Therefore less resources need to be reserved to satisfy a throughput constraint and a higher processor utilization can be obtained. Furthermore, we introduce a lock which is used to enforce mutual exclusive execution of tasks during a mode transition when beneficial. The effects of mutual exclusive execution are included in a Structured Variable-Rate Phased Dataflow (SVPDF) temporal analysis model which is used to determine whether adding a lock results in satisfaction of the throughput constraint. This model is generated from a sequential input specification of the application such that deadlock-free execution, even after the addition of locks, is guaranteed. The applicability and benefits of the approach are demonstrated using a WLAN 802.11g application which switches between a detection and a decoding mode. It is shown that the use of two locks improves the worst-case response times of 3 tasks such that they can share the same processor, which improves the utilization of this processor and frees 2 other processors.