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)
Section 1: Character Device Driver Basics
User-Kernel Communication Pathways
Handling Hardware Interrupts
Working with Kernel Timers, Threads, and Workqueues
Section 2: Delving Deeper

Measuring time servicing individual hardirqs

The hardirqs[-bpfcc] tool displays the total time spent servicing hardirqs (hardware interrupts). The following screenshot shows us running the hardirqs-bpfcc tool. Here, you can see the total time that was spent servicing hardirqs every 1 second (first parameter) for 3 seconds (second parameter):

Figure 4.14 – hardirqs-bpfcc showing the time that was spent servicing hardirqs every 1 second for 3 seconds

The following screenshot shows us using the same tool to generate a histogram of hard IRQ time distribution (via the -d switch):

Figure 14.15 – hardirqs-bpfcc -d showing a histogram

Notice how the majority of the network hardirqs (iwlwifi, 48 of them) take just between 4 to 7 microseconds to complete, though a few (three of them) take between 16 and 31 usecs.

You can find more examples of how to use the hardirqs[-bpfcc] tool at https://github...