tailieunhanh - Bài giảng Hệ điều hành nâng cao (Operating System-OS): Chương 5 - Phan Vĩnh Thuần

Chương 5 - process management. Bài giảng gồm có những nội dung chính sau: Principles of I/O hardware, principles of I/O software, I/O software layers, disks, clocks, character - oriented terminals, graphical user interfaces, network terminals, power management. | Chapter 5. CPU Scheduling OBJECTIVES To introduce CPU scheduling, which is the basis for multiprogrammed operating systems To describe various CPU-scheduling algorithms. To discuss evaluation criteria for selecting a CPU-scheduling algorithm for a particular system. . Basic Concepts A process is executed until it must wait, typically for the completion of some I/O request. The CPU then just sits idle. This waiting time is wasted. The objective of multiprogramming is to have some process running at all times, to maximize CPU utilization. When one process has to wait, the operating system takes the CPU away from that process and gives the CPU to another process. Scheduling of this kind is a fundamental operating-system function. . CPU-I/O Burst Cycle The success of CPU scheduling depends on an observed property of processes: Process execution consists of a cycle of CPU execution and I/O wait. Processes alternate between these two states. Process execution begins with a CPU burst. That is followed by an I/O burst, which is followed by another CPU burst, then another I/O burst, and so on. Eventually, the final CPU burst ends with a system request to terminate execution Figure . Alternating sequence of CPU and I/O bursts. . CPU Scheduler Whenever the CPU becomes idle, the operating system must select one of the processes in the ready queue to be executed. The selection process is carried out by the short-term scheduler (or CPU scheduler). CPU-scheduling decisions may take place under the following four circumstances: When a process switches from the running state to the waiting state (for example, as the result of an I/O request or an invocation of wait for the termination of one of the child processes) When a process switches from the running state to the ready state (for example, when an interrupt occurs) When a process switches from the waiting state to the ready state (for example, at completion of I/O). When a process terminates. When scheduling . | Chapter 5. CPU Scheduling OBJECTIVES To introduce CPU scheduling, which is the basis for multiprogrammed operating systems To describe various CPU-scheduling algorithms. To discuss evaluation criteria for selecting a CPU-scheduling algorithm for a particular system. . Basic Concepts A process is executed until it must wait, typically for the completion of some I/O request. The CPU then just sits idle. This waiting time is wasted. The objective of multiprogramming is to have some process running at all times, to maximize CPU utilization. When one process has to wait, the operating system takes the CPU away from that process and gives the CPU to another process. Scheduling of this kind is a fundamental operating-system function. . CPU-I/O Burst Cycle The success of CPU scheduling depends on an observed property of processes: Process execution consists of a cycle of CPU execution and I/O wait. Processes alternate between these two states. Process execution begins with a CPU .