How the spinlock is implemented is really not our concern here; the fact that the spinlock has a lower overhead than the mutex lock is of interest to us. How so? It's simple, really: for the mutex lock to work, the loser thread has to go to sleep. To do so, internally, the schedule() function gets called, which means the loser sees the mutex lock API as a blocking call! A call to the scheduler will ultimately result in the processer being context-switched off. Conversely, when the owner thread unlocks the lock, the loser thread(s) must be woken up; again, it will be context-switched back onto the processor. Thus, the minimal "cost" of the mutex lock/unlock operation is the time it takes to perform two context switches on the given machine. (See the Information Box in the next section.) By relooking at the preceding screenshot once more, we can determine a few things, including...
Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization
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Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization
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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.
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Current Title:
Linux Kernel Programming Part 2 - Char Device Drivers and Kernel Synchronization
Table of Contents (11 chapters)
Preface
Section 1: Character Device Driver Basics
Free Chapter
Writing a Simple misc Character Device Driver
User-Kernel Communication Pathways
Working with Hardware I/O Memory
Handling Hardware Interrupts
Working with Kernel Timers, Threads, and Workqueues
Section 2: Delving Deeper
Kernel Synchronization - Part 1
Kernel Synchronization - Part 2
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