Segment Fixed Priority Scheduling for Self Suspending Real Time Tasks
CARNEGIE-MELLON UNIV PITTSBURGH PA PITTSBURGH United States
Pagination or Media Count:
Recent trends in System-on-a-Chip show that an increasing number of special-purpose processors are being added to improve the efficiency of common operations. Unfortunately, the use of these processors may introduce suspension delays incurred by communication, synchronization, and external IO operations. When these processors are used in real-time systems, conventional schedulability analyses incorporate these delays in the worst-case executionresponse time, hence significantly reducing the schedulable utilization. This report describes schedulability analyses and proposes segment-fixed priority scheduling for self-suspending tasks. We model the tasks as segments of execution separated by suspensions. We start from providing response-time analyses for self-suspending tasks under Rate Monotonic Scheduling RMS. While RMS is shown to not be optimal, it can be used effectively in some special cases that we have identified. We then derive a utilization bound for the cases as a function of the ratio of the suspension duration to the period of the tasks. For general cases, we develop a segment-fixed priority scheduling scheme. Our scheme assigns individual segments different priorities and phase offsets that are used for phase enforcement to control the unexpected self-suspending nature.
- Administration and Management
- Computer Hardware