“This is the first day of my participation in the Gwen Challenge in November. See details of the event: The last Gwen Challenge in 2021”.

Are there many algorithms for process scheduling? We evaluate whether a process scheduling algorithm is good by the following criteria.

Criteria for process scheduling algorithms

  1. CPU usage: Indicates the percentage of the busy CPU time in the total CPU time.
  2. System throughput: number of jobs completed per unit of time (total jobs completed/total time spent).
  3. Turnaround time refers to the time interval from the time a job is submitted to the system until the job is completed (job completion time – job submission time). The operating system is more concerned with average turnaround time = total turnaround time for each job/number of jobs

A turnaround time is divided into four stages:

  1. The amount of time a job waits on an external backup queue for job scheduling (advanced scheduling),
  2. The time a process waits on the ready queue for process scheduling (low-level scheduling),
  3. The time a process takes to execute on the CPU,
  4. The amount of time a process waits for an I/O operation to complete.

On the basis of the turnaround time, we propose the weighted turnaround time and the average weighted turnaround time. The weighted turnaround time is = operation turnaround time/actual operation time. It has been mentioned above that the average turnaround time should be distinguished from the average turnaround time with rights. The average turnaround time with rights = the sum of the turnaround time with rights for each operation/the number of operations.

It seems very difficult to understand, but we can consider through calculation, the job turnaround time is certain, then the longer the running time of the job itself, the less the weight turnaround time, the same as the weight turnaround time, the less time the user satisfaction will be higher. When the weighted turnaround time is constant, the more jobs there are, the less turnaround time there is. The more jobs there are, the less time a single job needs. In other words, users of short jobs will be more satisfied.

Through the above criteria, we can evaluate the quality of a process scheduling algorithm