Book Image

Mastering Embedded Linux Programming

By : Chris Simmonds
Book Image

Mastering Embedded Linux Programming

By: Chris Simmonds

Overview of this book

Mastering Embedded Linux Programming takes you through the product cycle and gives you an in-depth description of the components and options that are available at each stage. You will begin by learning about toolchains, bootloaders, the Linux kernel, and how to configure a root filesystem to create a basic working device. You will then learn how to use the two most commonly used build systems, Buildroot and Yocto, to speed up and simplify the development process. Building on this solid base, the next section considers how to make best use of raw NAND/NOR flash memory and managed flash eMMC chips, including mechanisms for increasing the lifetime of the devices and to perform reliable in-field updates. Next, you need to consider what techniques are best suited to writing applications for your device. We will then see how functions are split between processes and the usage of POSIX threads, which have a big impact on the responsiveness and performance of the final device The closing sections look at the techniques available to developers for profiling and tracing applications and kernel code using perf and ftrace.
Table of Contents (22 chapters)
Mastering Embedded Linux Programming
About the Author
About the Reviewers

Preemptible kernel locks

Making the majority of kernel locks preemptible is the most intrusive change that PREEMPT_RT makes and this code remains outside of the mainline kernel.

The problem occurs with spinlocks, which are used for much of the kernel locking. A spinlock is a busy-wait mutex which does not require a context switch in the contended case and so is very efficient as long as the lock is held for a short time. Ideally, they should be locked for less than the time it would take to reschedule twice. The following diagram shows threads running on two different CPUs contending the same spinlock. CPU0 gets it first, forcing CPU1 to spin, waiting until it is unlocked:

The thread that holds the spinlock cannot be preempted since doing so may make the new thread enter the same code and deadlock when it tries to lock the same spinlock. Consequently, in mainline Linux, locking a spinlock disables kernel preemption, creating an atomic context. This means that a low priority thread that holds...