Operating System Support for Coexistence of Real-Time and Conventional Scheduling.

Abstract
The advent of multimedia calls for new scheduling paradigms to handle the combination of time-critical and conventional applications present on many multimedia systems. The scheduler of the Mach 3.0 Microkemel has heen rewritten to allow a wide spectrum of scheduling policies, from real-time through time-sharing to background, to be selected simultaneously for different tasks executing on the same processor. Scheduling policies can he set for a task or for individual threads within the task. The set of scheduling policies allowed on a processor or set of processors may be dynamically altered. Scheduling parameters can be set individually for each thread, task, or scheduling policy enabled on a processor. Each scheduling policy may have its own format for paiameters; they are not limited to integer priorities. New scheduling policies may be configured into a kernel and may he ordered in any way desired. The resulting system provides enough flexibility for experimentation with new scheduling regimes, yet is efficient enough to allow a reasonable number of scheduling policies to coexist. When configured with both real-time and timesharing schedulers, the system smoothly supports both conventional and time-critical applications.

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