Operating system
- 2. SCHEDULING CRITERIA There are many scheduling algorithms and various criteria to judge their performance some criteria are as follows: o CPU Utilization: CPU should be busy (from 0 to 100%) o Throughput: the number of process executed in a specified time period o Turnaround time: needed to execute a process o Waiting Time: amount of time a process has waited o Response Time: between request and response
- 3. A CPU SCHEDULING ALGORITHM MUST MAXIMIZE THE FOLLOWING CPU utilization should maximum Throughput should maximum
- 4. A CPU SCHEDULING ALGORITHM MUST MINIMIZE THE FOLLOWING: Waiting Time should minimum Response Time should minimum Turnaround Time should minimum
- 5. SCHEDULING ALGORITHMS: Below is the list of some well known algorithms First Come First Served (FCFS) scheduling- non preemptive Shortest job First(SJF) scheduling preemptive non preemptive Priority Scheduling preemptive non preemptive Round robin scheduling preemptive
- 6. TIMELINES: Scheduling is based on the information that is available at the give time. we need some ways to represent the state of the system and any process in it and how it change over time. Gantt chart are used for this purpose to present them in graphical way.
- 7. GANTT CHART 1st Process 2nd Process More Processes 1st process end time 2nd Process end time…… End time. Start time p1 end time p2end time……End time. First come First Served (FCFS) •Simplest •Similar to queue
- 9. Process Name Start Time Burst Time Process 1 0 24 Process 2 0 3 Process3 0 3 Example 1 Process1 Process2 Process3 0 24 27 30
- 10. FCFS The following table shows the waiting time for each process: Average Waiting time is(0+24+27)/3=17 Process name Arrival time Burst time Finish time Waiting time Process1 0 24 24 0 Process2 0 3 27 24 Process3 0 3 30 27
- 11. Gantt chart P1 P2 P3 0 3 6 30 Process Name Start Time Burst Time Process 2 0 3 Process 3 0 3 Process1 0 24 Example 2
- 12. Process name Arrival time Burst time Finish time Waiting time Process2 0 3 3 0 Process3 0 3 6 3 Process1 0 24 30 6 Average Waiting time is (0+3+6)/3= 3
- 13. Shortest Job First: Another way to scheduling jobs is to pick the job that will take least amount of time to complete, based on burst size. In this way the average waiting time reduced. •Normal SJF •Non preemptive • Preemptive
- 16. Non preemptive SJF Example: Process name Arrival time Burst time Process1 0 7 Process2 2 4 Process3 4 2 Process4 5 4
- 17. Process name Arrival time Burst time Finish time Waiting time Process1 0 7 7 0 Process2 2 4 13 7 Process3 4 2 9 3 Process4 5 4 17 8
- 18. Process name Arrival time Burst time Process1 0 7 Process2 2 4 Process3 4 1 Process4 5 4 Preemptive SJF Example 2
- 19. Process name Arrival time Burst time Finish time Waiting time Process1 0 7 16 9 Process2 2 4 7 1 Process3 4 1 5 0 Process4 5 4 11 2
- 20. Requires that each process should have priority associated with it. Priority scheduling: Priority scheduling Example for Non Preemptive Process name Burst Time Priority Process1 10 3 Process2 1 1 Process3 2 3 Process4 1 4 Process5 5 2
- 21. Process2 Process5 Process1 Process3 Process4 Priority scheduling Example Preemptive Process name Arrival time Burst time Priority Process1 0 10 3 Process2 2 1 1 Process3 4 2 2 Process4 6 1 4 Process5 8 5 5 Gantt Chart 0 1 6 16 18 ` 19
- 22. P1 P2 P1 P3 P1 P2 P5 Round robin scheduling Gantt Chart 0 2 3 4 6 13 14 19 Another way to schedule jobs is to assign a small amount of time to each process in which it executes. This time the unite is called time quantum or tie slice, the job is allocated to CPU for the quantum. when the time quantum expires, the process preempted from CPU and replaced by next process in the circle queue.
- 24. Process name Burst time Process1 24 Process2 3 Process3 3 Gantt Chart P1 P2 P3 P1 P1 P1 P1 P1 0 4 7 10 14 18 22 26 30 (10+7+30)/3=16
- 25. THANKS…..
Editor's Notes
- #2: Raeesa imtiaz