When you think about customizing the core of an Android system, you immediately think about customizing the Linux kernel. It manages CPU, sensors, radio, and display, and it's the starting point of every great system customization. As we already saw, modifying the kernel is no easy job, but with the right mindset, knowledge, and toolset, it can be a satisfying experience.
Every embedded system has its own customization possibilities and, when it comes to Android, most of the effort is focused on customizing the following:
Governors
I/O schedulers
CPU overclocking/underclocking
In Chapter 5, Customizing Kernel and Boot Sequence, we had an overview about governors, how they work, and how you can pick a different one for different scenarios. In this section, you will learn how to customize existing governors and how to add new ones to your systems.