Linux System Programming, 2nd Edition

Chapter 6. Advanced Process Management

Chapter 5 explained what a process is and what parts of the system it encompasses, along with system calls to create, control, and destroy it. This chapter builds on those concepts, beginning with a discussion of the Linux process scheduler and its scheduling algorithm, and then presenting advanced process management interfaces. These system calls manipulate the scheduling behavior of a process, influencing the scheduler’s behavior in pursuit of an application or user-dictated goal.

Process Scheduling

The process scheduler is the kernel subsystem that divides the finite resource of processor time among a system’s processes. In other words, the process scheduler (or simply the scheduler) is the component of a kernel that selects which process to run next. In deciding which processes can run and when, the scheduler is responsible for maximizing processor usage while simultaneously providing the illusion that multiple processes are executing concurrently and seamlessly.

In this chapter, we will talk a lot about runnable processes. A runnable process is one that is not blocked; a blocked process is one that is sleeping, waiting for I/O from the kernel. Processes that interact with users, read and write files heavily, or respond to network events tend to spend a lot of time blocked while they wait for resources to become available, and they are not runnable during those periods. Given only one runnable process, the job of a process scheduler is trivial: ...