5.2 Scheduling Criteria

Many criteria have been suggested for comparing CPU-scheduling algorithms.

• CPU utilization. We want to keep the CPU as busy as possible. Concep- tually, CPU utilization can range from 0 to 100 percent. 
• Throughput. One measure of work is the number of processes that are completed per time unit.
• Turnaround time. The interval from the time of submission of a process to the time of completion is the turnaround time.urnaround time is the sum of the periods spent waiting in the ready queue, executing on the CPU, and doing I/O.
• Waiting time. The CPU-scheduling algorithm does not affect the amount of time during which a process executes or does I/O. It affects only the amount of time that a process spends waiting in the ready queue. Waiting time is the sum of the periods spent waiting in the ready queue.
• Response time. In an interactive system, turnaround time may not be the best criterion. Often, a process can produce some output fairly early and can continue computing new results while previous results are being output to the user. Thus, another measure is the time from the submission of a request until the first response is produced. This measure, called response time, is the time it takes to start responding, not the time it takes to output the response.