Real-time scheduling using compact task graphs

Abstract

The generation of a real-time schedule from a task precedence graph is complex and time consuming. In order to improve the efficiency of generating schedules, we propose a scheduling algorithm based upon the compact task graph (CTG) representation. In addition to precedence constraints, a CTG explicitly expresses the potential for interleaving the execution of tasks on a single processor and overlapping the execution of task on multiple processors. The CTG is compact since it expresses the potential for overlapping and interleaving without the generation of smaller tasks. If a task cannot be scheduled to meet its deadline through interleaving and overlapping, then selected tasks are split into smaller tasks which increases the feasibility, and hence the complexity, of scheduling the task. Thus, in effect our approach increases the complexity of scheduling a usual task graph only if it is essential. Our results demonstrate that a significant reduction in the time of scheduling is achieved using CTGs and our algorithms that exploit the CTGs. We also show how CTGs can be used for distributed on-line scheduling.