Preference-Oriented Fixed-Priority Scheduling for Real-Time Systems

Most real-time scheduling algorithms prioritize tasks solely based on their timing parameters and cannot effectively handle them when they have different execution preferences. In this paper, for a set of periodic tasks, where some tasks are preferably executed as soon as possible (ASAP) and others as late as possible (ALAP), we investigate preference-oriented fixed-priority scheduling algorithms. Specifically, following the idea in dual-priority scheduling, we derive promotion times for ALAP tasks (only). Then, we devise a dual-queue based fixed-priority scheduling algorithm that retains ALAP tasks in the waiting queue until their promotion times to delay their executions while putting ASAP tasks into the ready queue immediately once they arrive for early execution. We also investigate online techniques to further expedite (delay) the executions of ASAP (ALAP) tasks, respectively. Our evaluation results show that the dual-queue technique with ALAP tasks' promotion times can effectively address the execution preferences of both ASAP and ALAP tasks, which can be further improved at runtime with wrapper-task based slack management. Our technique is shown to yield clear advantages over a simple technique that periodically inserts idle intervals to the schedule before ALAP tasks are executed.