Compiler Aided Ticket Scheduling (CATS) For Non-Preemptive Embedded Systems

A key challenge in designing realtime systems for non- preemptive architectures is the timely guarantee of the exe- cution of periodic tasks, together with non-periodic tasks. The main challenge of scheduling tasks in such systems results from the conflict between the requirement to exe- cute periodic tasks at specific time intervals, versus the re- quirement to yield the CPU to non-periodic tasks. The non- periodic tasks may not relinquish the CPU, thus jeopar- dizing the periodic tasks deadlines. This paper describes a technique that can be used by any given non-preemptive scheduler in order to produce a finer-grained schedule for the system task set. The technique increases the CPU uti- lization and improves the overall system performance. Com- piler Aided Ticket Scheduling (CATS), provides compiler generated primitives that are used by the scheduler at run- time, allowing it to better decide about which task to run next. The enhanced scheduler remains "safe" in the sense that the chosen task is guaranteed to yield the processor before the next periodic task must be executed. This paper also proposes a programming model which enables the de- veloper to systematically tune the embedded system tasks to meet the scheduling requirements.