Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization

By: Kaiwan N. Billimoria

Overview of this book

Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization is an ideal companion guide to the Linux Kernel Programming book. This book provides a comprehensive introduction for those new to Linux device driver development and will have you up and running with writing misc class character device driver code (on the 5.4 LTS Linux kernel) in next to no time. You'll begin by learning how to write a simple and complete misc class character driver before interfacing your driver with user-mode processes via procfs, sysfs, debugfs, netlink sockets, and ioctl. You'll then find out how to work with hardware I/O memory. The book covers working with hardware interrupts in depth and helps you understand interrupt request (IRQ) allocation, threaded IRQ handlers, tasklets, and softirqs. You'll also explore the practical usage of useful kernel mechanisms, setting up delays, timers, kernel threads, and workqueues. Finally, you'll discover how to deal with the complexity of kernel synchronization with locking technologies (mutexes, spinlocks, and atomic/refcount operators), including more advanced topics such as cache effects, a primer on lock-free techniques, deadlock avoidance (with lockdep), and kernel lock debugging techniques. By the end of this Linux kernel book, you'll have learned the fundamentals of writing Linux character device driver code for real-world projects and products.
Table of Contents (11 chapters)
1
Section 1: Character Device Driver Basics
3
User-Kernel Communication Pathways
5
Handling Hardware Interrupts
6
Working with Kernel Timers, Threads, and Workqueues
7
Section 2: Delving Deeper

Lock statistics

A lock can be contended, which is when, a context wants to acquire the lock but it has already been taken, so it must wait for the unlock to occur. Heavy contention can create severe performance bottlenecks; the kernel provides lock statistics with a view to easily identifying heavily contended locks. Enable lock statistics by turning on the CONFIG_LOCK_STAT kernel configuration option (without this, the /proc/lock_stat entry will not be present, the typical case on most distribution kernels).

The lock stats code takes advantage of the fact that lockdep inserts hooks into the locking code path (the __contended__acquired, and __released hooks) to gather statistics at these crucial points. The neatly written kernel documentation on lock statistics (https://www.kernel.org/doc/html/latest/locking/lockstat.html#lock-statistics) conveys this information (and a lot more) with a useful state diagram; do look it up.

...