As seen in the companion guide Linux Kernel Programming - Chapter 11, The CPU Scheduler – Part 2, in the Converting mainline Linux into an RTOS section, we covered the real-time patch for Linux (RTL), which allows you to patch, configure, build, and run Linux as an RTOS! If you're hazy on this, please refer back to this. We won't repeat the same information here.
The Real-Time Linux (RTL) project's work has been steadily back-ported into the mainline Linux kernel. One of the key changes wrought by RTL was merging the threaded interrupts feature into the mainline kernel. This occurred in kernel version 2.6.30 (June 2009). This technology does something that, at first glance, seems very weird: it "converts" the hardware interrupt handler into, essentially, a kernel thread.
As you will learn in the next chapter, a kernel thread is really very similar...
