TIME-DRIVEN SCHEDULING MODEL FOR REAL-TIME OPERATING SYSTEMS.

Process scheduling in real-time systems has almost invariably used one or more of three algorithms, namely, fixed priority, FIFO, or round robin. The notion that the primary distinguishing characteristic of a real-time system is the concept that completion of a process or a set of processes has a value to the system which can be expressed as a function of time is discussed. This notion is described in terms of a time-driven scheduling model for real-time operating systems and provides a tool for measuring the effectiveness of most of the currently used process schedulers in real-time systems. Applying this model, a multiprocessor real-time system simulator was constructed with which a number of well-known scheduling algorithms such as Shortest Process Time (SPT), Deadline, Shortest Slack Time, FIFO, and a fixed priority scheduler are measured with respect to the resulting total system values. This approach to measuring the process scheduling effectiveness is a first step in the longer term effort to produce a scheduler which will explicitly schedule real-time processes in such a way that their execution times maximize their collective value to the system.