Running Linux as an RTOS – an introduction

Mainline or vanilla Linux (the kernel you download from https://kernel.org, or even a typical Linux Git kernel tree) is decidedly not an RTOS; it’s a General Purpose Operating System (GPOS; as is Windows, macOS, and Unix). In an RTOS, where hard real-time (RT) characteristics come into play, not only must the software obtain the correct result but there are deadlines associated with doing so; it must guarantee it meets these deadlines, every single time.

One can very broadly categorize an OS based on its RT characteristics in this manner (see Figure 11.16); at the left extreme are the non-RT OSs, and at the right extreme is the RTOS:

Figure 11.16: Categorizing an OS on the RT scale

The mainline or “vanilla” Linux OS, though not an RTOS, does a tremendous job performance-wise without even breaking a sweat. It easily qualifies as being a soft real-time OS: one where deadlines are met most of the...