Preemptive Phased Execution Models with Scratchpad Memory Requirements

There is currently a widespread interest in using phased execution models in the design of real-time systems, stimulated by their ability to reduce contention in accessing shared resources. The main beneficiary of such approaches is the wide category of Commercial Off-The-Shelf (COTS) multi-core systems, where complexity is an underlying issue. However, the advantage of predictability comes at a cost, which often resides in the additional decisions that are usually made when using phased execution models. One such decision is employing non-preemptive scheduling; as is well known, this leads to NP-hardness for most instances of the scheduling problem, while preemption can avoid this level of complexity in many cases. It is no surprise, then, that recent efforts have attempted to explore the possibilities offered by preemptive scheduling in combination with phased execution models. Unlike existing work, the current paper focuses on the scratchpad memory consumption in preemptive phased execution models. The starting point, the model introduced by the authors of a previous article, was meant for the general analysis of the efficiency of preemptive scheduling in phased execution models. Notably, two methods for handling intermediate data are introduced, namely, the Waiting Time Minimizing Preemption (WMPM) and the Overhead Minimizing Preemption (OMPM). The current paper analyses the requirements of each approach in terms of scratchpad memory. It also introduces a hybrid method, in order to achieve a finer balance between memory consumption and schedulability constraints.