explain any three policies for process scheduling

Question

Explain any three policies for process scheduling that uses resource consumption information.

All three policies for process scheduling are explained below in brief:

1. First-come First-served (FCFS) (FIFO)

- Jobs are scheduled in order of coming

- Nonpreemptive

• Problem:

- Average waiting time can be huge if small jobs wait behind long ones

- May cause poor overlap of I/O and CPU and convoy consequences

2. Shortest Job First (SJF)

- Select the job with the shortest next CPU burst

-For minimizing average waiting time provably optimal

• Problem:

- Not possible knowing the length of the next CPU burst

3. Round Robin (RR)

- Frequently used for timesharing

- Ready queue is function as a circular queue (FIFO)

- Each process is specified a time slice termed as a quantum

- This is run for the quantum or till it blocks

- RR allocates the CPU uniformly or fairly across each participant. If average queue length is n, all participants get 1/n

- Since the time quantum grows, RR becomes FCFS

- Smaller quanta are usually desirable, since they improve response time

• Problem:

- Context-switch over-head of frequent context-switch