Jitter control in on-line scheduling of dependent real-time tasks

A typical characteristic of real-time systems is concurrent processing of tasks under strict timing requirements. These timing requirements may impose not only direct constraints, such as deadlines, but also indirect timing constraints in terms of inter-task dependencies. However scheduling policies which can deal with some of these constraints effectively are limited, especially for the on-line context, and are not widely known within the real-time community. In this context, this paper presents a technique to control execution irregularities, namely, jitter. The technique is based on the modification of task temporal parameters in the paradigm of the well known Deadline Monotonic (DM) and Earliest Deadline First (EDF) algorithms. The technique presents a way either to remove jitter completely (in the case of regularity constrained tasks) or to bound jitter releases. Moreover, the approach takes into account temporal dependencies of tasks on one another.