Runtime feasibility check for non-preemptive real-time periodic tasks

The most important requirement for real-time systems is the capability to support the timely execution of applications. Real-time scheduling over a single processor has been widely studied in the last thirty years, and it has been proven that the non-preemptive version of Earliest Deadline First (EDF) algorithm is optimal [1], in the sense that if a set of tasks is schedulable, it is also schedulable using EDF. EDF scheduler always selects and executes a task having the earliest deadline. Most non-preemptive real-time systems favor the EDF scheduler for its easy feasibility check and optimal schedulability. In EDF scheduling, however, scheduler leaves no chance for other feasible alternative task sequences to be selected. Fig. 1 shows an example in which an alternative task execution sequence is more preferable than