On-line sporadic task scheduling in hard real-time systems

We propose a set of scheduling procedures for dealing with the sporadic task scheduling in a dynamic periodic system. For this we mean a system in which periodic tasks change their parameters dynamically (at run-time), in an unpredictable way. So, the off-line periodic task set will be different from the current periodic task set. It means that the task schedulability tests in such systems have to be made on-line. On the other hand, on-line evaluations in hard real-time systems must be done in a fast way, once the overhead incurred in these evaluations may jeopardize the tasks timing requirements. As it is common that exact tests, providing necessary and sufficient conditions for validating the schedule, are intractable algorithms (EXPTIME), they can not support on-line decisions. Then, our goal is to provide a sufficient condition for on-line scheduling tests which is fast (PTIME) and can be reasonably useful compared to the exact condition. We present a series of simulation runs that confirm the usefulness of our approach