Improving the Schedulability of Mixed Criticality Cyclic Executives via Limited Task Splitting

Mixed Criticality workloads present a challenging paradigm which requires equal consideration of functional separation and efficient platform usage. As more powerful platforms become available the consolidation of previously federated functionality becomes highly desirable. Such platforms are becoming increasingly multi-core in nature bringing challenges in addition to those of isolation and utilisation. Cyclic Executives (CE) are used extensively in industry to schedule highly critical functionality in a manner which aids certification. The CE paradigm may be applied to the mixed criticality case making use of a number of features to ensure the sufficient separation of different levels of criticality. While previous work has considered the separation of criticality levels, this work focuses on providing high system utilisation. One of the significant challenges of such an implementation is the allocation of work (tasks) to minor cycles and cores. This work considers such an allocation problem and presents a means of testing schedulability using Linear Programming (LP) tools. Toward the aim of high system utilisation we consider how tasks of different criticality levels might be split, in some limited way, in order to increase the overall schedulability. We show that even minimal task splitting can drastically release slack previously unusable due to isolation requirements, which in turn provides a significant increase in schedulability.