Improving Task Responsiveness with Limited Preemptions

The optimality of preemptive EDF scheduling with relation to the achievable system utilization is a clear advantage of this scheduling policy for single processor real-time systems. However, recent works suggested that the run-time behavior of EDF might be improved by limiting the preemption support only to particular time instants, dividing each task into a sequence of non-preemptive chunks of execution, without affecting the schedulability of the system. In this paper, we will take a closer look to limited preemption EDF scheduling (LP-EDF), evaluating the potential advantages offered by this policy in terms of response-time reduction and improved control performances. In particular, we will show how to increase the responsiveness of a control application by placing non-preemptive regions of maximal length at the end of the code of selected tasks. The effectiveness of the proposed method will be proved both analytically and by extensive simulations.