Overhead effects in real-time preemptive schedules

The hard real-time schedulability of dependent task-graphs is studied for single bus homogeneous multiprocessor systems. A model which includes interrupts and context switching as well as bus contention is developed. The model captures real-time operating system effects aimed at realistically modeling both intra-processor and inter-processor communications. A robust scheduler is used to assess the impact of interrupt service time (IST) and context switching time (CST) on schedulability. For the class of task-graphs studied, it is shown that schedulability is a nonlinear function of only the weighted sum of IST and CST.