TASK-SCHEDULING POLICIES FOR REAL-TIME SYSTEMS

The software of modern real-time embedded systems is frequently very complex. Many applications occupy a megabyte or more of code.1 Application programmers are increasingly adopting a multi-tasking design approach to produce reliable and predictable software. To support such implementations, system support in the form of real-time operating systems or real-time executives is required, and central to these is the task scheduler and its associated scheduling policies. Scheduling software must be optimized for small size, fast interrupt response and fast context switching. These requirements are very demanding of scheduling policy and implementation. It is not sufficient that a scheduler functions as required; it must also perform in 'real-time'. This paper describes a variety of task scheduling policies for use with real-time embedded systems, including commonly used practical strategies as well as new ideas from the research community. The performance of these policies is compared using simulation techniques.