Decentralized Real-Time Scheduling

Abstract : This document describes experiments designed to evaluate the behavior and performance of various scheduling policies for the Alpha real-time distributed operating system. Alpha is an adaptable decentralized operating system being developed as a part of the Archons project's on-going research into real-time distribution systems. Timely completion of an application's computational activities is one of the most important functions of a real-time system. Therefore, the proper scheduling of those activities is of critical importance. The Alpha programming model provides simple mechanisms for an application to specify its timeliness requirements. The scheduler may consider this time constraint information when scheduling activities for execution. To gauge the effectiveness of Alpha as an operating system for real-time applications, an understanding of its scheduling facility is necessary. To this end, a study of the effects of various different scheduling policies was made. To evaluate these policies, a real-time application was created to serve as an experimental workload. The application was designed to simplify the modeling of tasks with a wide range of timeliness requirements and to provide a visual indication of scheduler performance. Alpha provides a clean well-defined interface between the scheduling subsystem and the kernal proper. (KR)