Linux Kernel Development, Third Edition

11. Timers and Time Management

The passing of time is important to the kernel. A large number of kernel functions are time-driven, as opposed to event-driven.¹ Some of these functions are periodic, such as balancing the scheduler runqueues or refreshing the screen. They occur on a fixed schedule, such as 100 times per second. The kernel schedules other functions, such as delayed disk I/O, at a relative time in the future. For example, the kernel might schedule work for 500 milliseconds from now. Finally, the kernel must also manage the system uptime and the current date and time.

¹ More accurately, time-driven events are also event-driven—the event being the passing of time. In this chapter, however, we single out time-driven events because ...