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

Load balancing interrupts and IRQ affinity

First off, on a multicore (SMP) system, the way that hardware interrupts are routed to CPU cores tends to be very board and interrupt controller-specific. Having said that, the generic IRQ layer on Linux provides a very useful abstraction: it allows for (and implements) interrupt load balancing so that no CPUs (of set of CPUs) gets overloaded. There's even frontend utilities, irqbalance(1) and irqbalance-ui(1), that allow the admin (or root user) to perform IRQ balancing (irqbalance-ui is a ncurses frontend to irqbalance).

Can you change the interrupts that have been sent to a processor core(s)? Yes, via the /proc/irq/IRQ/smp_affinity pseudofile! It's a bitmask specifying the CPUs that this IRQ is allowed to be routed to. The trouble is that the default setting is to always allow all CPU cores to handle the interrupt by default. For example, on a system with eight cores, the value...