A Scheduling Technique Providing a Strict Isolation of Real-time Threads

Highly dynamic programming environments for embedded real-time systems require a strict isolation of real-time threads from each other to achieve dependable systems. We propose a new real-time scheduling technique, called guaranteed percentage (GP) scheme that assigns each thread a specific percentage of the processor power. A hardware scheduler in conjunction with a multithreaded processor guarantees the execution of instructions of each thread according to their assigned percentages within a time interval of 100 processor cycles. We compare performance and implementation overhead of GP scheduling against fixed priority preemptive (FPP), earliest deadline first (EDF), and least laxity first (LLF) scheduling using several benchmarks on our Komodo microcontroller that features a multithreaded Java processor kernel. Our evaluations show that GP scheduling reaches a speed-up similar to EDF and FPP but worse than LLF. However, its hardware implementation costs are still reasonable, whereas the LLF overhead is prohibitive. Only GP reaches the isolation goal among the examined scheduling schemes.