An evolution is happening in the way that operating systems support the real-time requirements of their applications. The need to run real-time applications such as multimedia in the same environment as complex non-real-time servers and applications has motivated much interest in restructuring existing operating systems. Many issues related to thread scheduling and synchronization have been investigated. However, little consideration has been given to the flexibility and modularity required in the support of application-level scheduling needs, although it is well known that application requirements are diverse. In this paper, we describe a real-time scheduling abstraction which provides modularity and flexibility to the scheduling support of operating systems. Our design has been implemented using the Mach 3.0 kernel and a locally developed multiprocessor kernel (the r-kernel) as development platforms. © 1997 John Wiley & Sons, Ltd.

A vital role of real-time kernels is to help applications meet real-time requirements. The common approach in existing kernel design methodology has been to replace the scheduler in the kernel according to the needs of the application. As new real-time applications with unconventional scheduling requirements continue to emerge, constantly changing the kernel results in it becoming less stable and less maintainable. We discuss the modularity problems associated with this adhoc approach. We propose a kernel design which solves many of the problems by providing a common real-time task model for all real-time applications. This model allows for much more flexibility in the implementation of application-level schedulers and at the same time encourages modularity in kernel and application design. The model has been implemented using the Mach 3.0 kernel as a development platform. The flexibility of our solution is illustrated by considering the demands placed on the kernel by a modern multimedia application.>