In October, 2004 the authors of this paper announced a Real-Time Linux Kernel prototype on the Linux Kernel mailing list. The Real-Time Linux prototype introduced preemptible locking into the Linux kernel, and allowed task preemption to occur while tasks were executing within critical sections, resulting in a dramatic improvement in the Real-Time response of the Linux kernel.

Ingo Molnar reviewed the preemptible locking prototype and quickly implemented a preemptible kernel on top of his existing Voluntary Preemption project. This effort gave rise to the Real-Time preemption patch, which is currently available for download here.

This paper examines the foundations of the Real-Time Linux kernel, focusing in detail on thread-context interrupt handling, replacement of non-preemptible locking with preemptible mutex-based locks, priority-inheritance, virtualization of interrupt-disable, integration of high-resolution timers, as well as current development on user-space extensions of the kernel real-time mutex.

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