Fast Linux bootup using non-intrusive methods for predictable industrial embedded systems

Fast kernel boot-time is one of the major concerns in industrial embedded systems. Application domains where boot time is relevant include (among others) automation, automotive, avionics etc. Linux is one of the big players among operating system solutions for general embedded systems, hence, a relevant question is how fast Linux can boot on typical hardware platforms (ARM9) used in such industrial systems. One important constraint is that this boot-time optimization should be as nonintrusive as possible. The reason for this comes from the fact that industrial embedded systems typically have high demands on reliability and stability. For example, adding, removing or changing critical source-code (such as kernel or initialization code) is impermissible. This paper shows the steps towards a fast-booting Linux kernel using non-intrusive methods. Moreover, targeting embedded systems with temporal constraints, the paper shows how fast the real-time scheduling framework ExSched can be loaded and started during bootup. This scheduling framework supports several real-time scheduling algorithms (user defined, multi-core, partitioned, fixed-priority periodic tasks etc.) and it does not modify the Linux kernel source code. Hence, the non-intrusive bootup optimization methods together with the un-modified Linux kernel and the non-patched real-time scheduler module offers both reliability and predictability¹.