Round Robin scheduling

ROUND-ROBIN SCHEDULING

One of the oldest, simplest, fairest and most widely used algorithms is round robin (RR).

In the round robin scheduling, processes are dispatched in a FCFS manner but are given a limited amount of CPU time called a quantum.

If a process does not complete before its quantum time expires, the CPU is preempted and given to the next process waiting in a queue. The preempted process is then placed at the back of the ready list.



Round Robin Scheduling is preemptive (at the end of time-slice).

The quantum too short causes too many context switches and lower the CPU efficiency. On the other hand, setting the quantum too long may cause poor response time.


In any event, the average waiting time under round robin scheduling is often quite long.

For Example:
RR: Quantum=15
Job
Execution Time
Arrival Time
0
75
0
1
40
10
2
25
10
3
20
80
4
45
85

RR: Average waiting time calculation

RR: Average turnaround time calculation

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