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Unit 5: Scheduling
Figure 5.5: Round-Robin Scheduling Notes
P 2 P 3
4 time 2 time
units units
2 units 2 units
P 1 P 4
CPU 3 time 3 time
Running units units
2 units 2 units
2 units 2 units
P 8 P 5
2 time 3 time
units units
2 units 2 units
P 7 P 6
4 time 5 time
units units
Advantages
Simple, low overhead, works for interactive systems
Disadvantages
1. If quantum is too small, too much time wasted in context switching
2. If too large (i.e., longer than mean CPU burst), approaches FCFS
Example: Example of RR with Time Quantum = 20
Process Burst Time
P 53
1
P 17
2
P 68
3
P 24
4
The Gantt chart is:
Typically, higher average turnaround than SJF, but better response
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