what is CPU Scheduling Criteria in operating system

Scheduling Criteria:

There are many different criterias to check when considering the "best" scheduling algorithm :
·         CPU utilization
To make out the best use of CPU and not to waste any CPU cycle, CPU would be working most of the time(Ideally 100% of the time). Considering a real system, CPU usage should range from 40% (lightly loaded) to 90% (heavily loaded.)
·         Throughput
It is the total number of processes completed per unit time or rather say total amount of work done in a unit of time. This may range from 10/second to 1/hour depending on the specific processes.
·         Turnaround time
It is the amount of time taken to execute a particular process, i.e. The interval from time of submission of the process to the time of completion of the process(Wall clock time).
TAT= CT-AT
·         Waiting time
The sum of the periods spent waiting in the ready queue amount of time a process has been waiting in the ready queue to acquire get control on the CPU.
WAT= TAT-BT
·         Load average
It is the average number of processes residing in the ready queue waiting for their turn to get into the CPU.
·         Response time
Amount of time it takes from when a request was submitted until the first response is produced. Remember, it is the time till the first response and not the completion of process execution(final response).
RT= (WAT-BT)/BT

In general CPU utilization and Throughput are maximized and other factors are reduced for proper optimization.

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