Efficient exact Boolean schedulability tests for fixed priority preemption threshold scheduling

摘要

Fixed priority preemption threshold scheduling (PTS) is effective in scalable real-time system design, which requires system tuning processes, where the performance of schedulability tests for PTS matters much. This paper proposes five methods for efficient exact Boolean schedulability tests for PTS, which returns the Boolean result that tells whether the given task is schedulable or not We regard the sufficient test for fully preemptive fixed priority scheduling (FPS) and the early exit in the response time calculations as the conventional approach. We propose (1) a new sufficient test, (2) new initial values for the start/finish times, (3) precalculation of the interference time within the start time, (4) incremental start/finish time calculation, and (5) early exits in start/finish time calculations. These are based on some previous work for FPS. The new initial start time, pre-calculation, and the incremental calculations also can be used for the exact response time analysis for PTS. Our empirical results show that the overall proposed methods reduce the iteration count/run time of the conventional test by about 60%/40% regardless of the number of tasks and the total utilization.