Module 5 - CPU scheduling. CPU scheduling is the basis of multiprogrammed operating systems. By switching the CPU among processes, the operating system can make the computer more productive. In this chapter, we introduce the basic scheduling concepts and discuss in great length CPU scheduling. FCFS, SJF, Round-Robin, Priority, and the other scheduling algorithms should be familiar to the students. | Lecture Operating system concepts Fifth edition Module 5 - Avi Silberschatz Peter Galvin Module 5 CPU Scheduling Basic Concepts Scheduling Criteria Scheduling Algorithms Multiple-Processor Scheduling Real-Time Scheduling Algorithm Evaluation Silberschatz and Galvin 1999 Basic Concepts Maximum CPU utilization obtained with multiprogramming CPU I O Burst Cycle Process execution consists of a cycle of CPU execution and I O wait. CPU burst distribution Silberschatz and Galvin 1999 Alternating Sequence of CPU And I O Bursts Silberschatz and Galvin 1999 Histogram of CPU-burst Times Silberschatz and Galvin 1999 CPU Scheduler Selects from among the processes in memory that are ready to execute and allocates the CPU to one of them. CPU scheduling decisions may take place when a process 1. Switches from running to waiting state. 2. Switches from running to ready state. 3. Switches from waiting to ready. 4. Terminates. Scheduling under 1 and 4 is nonpreemptive. All other scheduling is preemptive. Silberschatz and Galvin 1999 Dispatcher Dispatcher module gives control of the CPU to the process selected by the short-term scheduler this involves switching context switching to user mode jumping to the proper location in the user program to restart that program Dispatch latency time it takes for the dispatcher to stop one process and start another running. Silberschatz and Galvin 1999 Scheduling Criteria CPU utilization keep the CPU as busy as possible Throughput of processes that complete their execution per time unit Turnaround time amount of time to execute a particular process Waiting time amount of time a process has been waiting in the ready queue Response time amount of time it takes from when a request was submitted until the first response is produced not output for time-sharing environment Silberschatz and Galvin 1999 Optimization Criteria Max CPU utilization Max throughput Min turnaround time Min waiting time Min response time .
