Engineering and Analysis of Fixed Priority Schedulers

| Scheduling theory holds great promise as a means to a priori validate timing correctness of real-time applications. However, there currently exists a wide gap between scheduling theory and its implementation in operating system kernels running on speci c hardware platforms. The implementation of any particular scheduling algorithm introduces overheadand blocking components whichmust be accounted for in the timing correctness validation process. This paper presents a methodology for incorporating the costs of scheduler implementation within the context of xed priority scheduling algorithms. Both event-driven and timerdriven scheduling implementations are analyzed. We show that for the timer-driven scheduling implementations the selection of the timer interrupt rate can dramatically a ect the schedulability of a task set, and we present a method for determining the optimal timer rate. We analyzed both randomly generated and two well de ned task sets and found that their schedulability can be signi cantly degraded by the implementation costs. Task sets that have ideal breakdown utilization over 90%may not even be schedulable when the implementation costs are considered. This work provides a rst step towards bridging the gap between realtime scheduling theory and implementation realities. This gap must be bridged for any meaningful validation of timing correctness properties of real-time applications. Keywords| Real-time, scheduling, periodic, schedulability, feasibility.