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

A key challenge in designing realtime systems for nonpreemptive architectures is the timely guarantee of the execution 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 execute periodic tasks at specific time intervals, versus the requirement to yield the CPU to non-periodic tasks. The nonperiodic tasks may not relinquish the CPU, thus jeopardizing 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 utilization and improves the overall system performance. Compiler Aided Ticket Scheduling (CATS), provides compiler generated primitives that are used by the scheduler at runtime, 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 developer to systematically tune the embedded system tasks to meet the scheduling requirements.