CPU scheduling is a relatively simple idea which is important; because in a single processor system; the process must wait before being executed for the completion of some I/O request; resulting in the waste or loss of processor time as it left idle.
SCHEDULING CRITERIA:
The criteria used by the algorithm for CPU or process scheduling are as follows;
CPU utilization:
First comes utilization. CPU consumption can vary from 0 to 100 percent. In a genuine or actual system; it should vary from “40 percent (for a lightly loaded system) to 90 percent (for a heavily used system)”; as the CPU should always be kept busy. [2]
Throughput:
Secondly, The work done on the CPU can be measured as the number of processes; that are completed per time unit is called throughput. This rate may be one process per 60 minutes for longer processes; but for short communication, it may be ten processes per one second.
Turnaround time:
Also used as (TAT) is the period from the time of submission of a process to the time of completion of a process. It is the sum of the time or the total amount of time spent by a process in “waiting to get into memory; waiting in the ready queue, executing on the CPU, and doing I/O”.
Waiting time:
Also used as (AT) The scheduling algorithm does not influence or change the amount of time during which a process executes; or does Input/Output but it affects only the quantity of time that a process is in waiting in the queue. The time spent waiting in the ready queue is simply defined as waiting time.
Response time:
Also used as (RT). Lastly, Turnaround time may not be the best measure in some systems. A process can produce some output quite early; can continue computing new results at the same time the earlier results are being output to the user.