An open system allows independently developed hard real-time applications to run together with non-real-time applications and supports their reconfiguration at run-time. The open system always accepts non-real-time applications, but it never accepts a real-time application that may not be schedulable in the system. Once a real-time application is accepted, its schedulability is guaranteed regardless of the behaviors of other applications that execute concurrently in the system.

The paper describes the design and implementation of an open system in Linux and evaluates its performance. The implementation consists of three key components: a two-level kernel scheduler, a common system service provider, and real-time application programming interface (RTAPI). In Open real-time Linux, real-time applications can use existing Linux system resources and services, and there is no need to suspend the kernel in order to switch between real-time and non-real-time mode. The performance evaluation of Open Real-time Linux shows that its overhead of context switching outperforms any other available real-time linux system.

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