Operating System 5

CPU Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Basic Concepts ,[object Object],[object Object],[object Object]

CPU-I/O Burst Cycle Process A Process B

Schedulers ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

CPU Scheduler ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Dispatcher ,[object Object],[object Object],[object Object],[object Object],[object Object]

Scheduling Criteria ,[object Object],[object Object],[object Object],[object Object],[object Object]

“ The perfect CPU scheduler” ,[object Object],[object Object],[object Object],[object Object],[object Object]

Scheduling Algorithms FCFS ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

First Come First Served Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Waiting time for P 1 = 0; P 2 = 24; P 3 = 27 Average waiting time: (0 + 24 + 27)/3 = 17 Waiting time for P 1 = 6 ; P 2 = 0 ; P 3 = 3 Average waiting time: (6 + 0 + 3)/3 = 3 P 1 P 3 P 2 6 3 30 0 P 1 P 2 P 3 24 27 30 0

Shortest-Job-First (SJR) Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object]

Shortest Job First Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],P 1 P 3 P 2 7 P 1 (7) 16 0 P 4 8 12 Average waiting time = (0 + 6 + 3 + 7)/4 = 4 2 4 5 P 2 (4) P 3 (1) P 4 (4) P 1 ‘s wating time = 0 P 2 ‘s wating time = 6 P 3 ‘s wating time = 3 P 4 ‘s wating time = 7

Shortest Job First Scheduling Cont’d ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Average waiting time = (9 + 1 + 0 +2)/4 = 3 P 1 (7) P 2 (4) P 3 (1) P 4 (4) P 1 ‘s wating time = 9 P 2 ‘s wating time = 1 P 3 ‘s wating time = 0 P 4 ‘s wating time = 2 P 1 (5) P 2 (2) P 1 P 3 P 2 4 2 11 0 P 4 5 7 P 2 P 1 16

Shortest Job First Scheduling Cont’d ,[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Shortest Job First Scheduling Cont’d

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Priority Scheduling

Round Robin (RR) ,[object Object],[object Object]

[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Round Robin Scheduling Average wait time = (81+20+94+97)/4 = 73 57 20 37 57 24 40 40 17 P 1 (53) P 2 (17) P 3 (68) P 4 (24) P 1 (33) P 1 (13) P 3 (48) P 3 (28) P 3 (8) P 4 (4) P 1 P 2 P 3 P 4 P 1 P 3 P 4 P 1 P 3 P 3 0 20 37 57 77 97 117 121 134 154 162

[object Object],[object Object],[object Object],[object Object],Round Robin Scheduling

Turnaround Time Varies With The Time Quantum TAT can be improved if most process finish their next CPU burst in a single time quantum.

Multilevel Queue ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Multi-level Feedback Queues ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Example of Multilevel Feedback Queue ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Multiple-Processor Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Thread Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object]

Linux Scheduling ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

The Relationship Between Priorities and Time-slice length

List of Tasks Indexed According to Prorities

Conclusion ,[object Object],[object Object],[object Object],[object Object]

References ,[object Object],[object Object],[object Object],[object Object],[object Object]

Operating System 5

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Operating System 5