1. CHAPTER 2 PROCESSOR SCHEDULING PART III
by Uğur HALICI

2. 2.3.2 Shortest-Process-First (SPF)
In this method, the processor is assigned to the process with the smallest execution (processor burst) time.
This requires future knowledge of the execution time.
In our examples, it is given as a table but actually these burst times are not known by the OS. So it makes prediction.
One approach for this prediction is using the previous processor burst times for the processes in the ready queue and then the algorithm selects the shortest predicted next processor burst time.

3. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
SPF
RQ:
A:4
next_cpu_burst
FCFS

4. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8
Proc_id : next_cpu_burst

5. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8
C:2

6. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8
C:2

7. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8

8. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
D:1

9. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
D:1
A:4

10. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
D:1
A:4
C:2

11. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
D:1
A:4
C:2

12. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4
C:2
B:8

13. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4
B:8
D:1

14. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4
B:8
D:1

15. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4
B:8

16. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8
D:1

17. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8
D:1

18. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
B:8

19. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4

20. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:
A:4

21. 2.3.2 Shortest-Process-First (SPF)
Arrival time
1st exec
1st I/O
2nd exec
2nd I/O
3rd exec A 4 B 2 8 1 - C 3 D 7
RQ:

22. 2.3.2 Shortest-Process-First (SPF)
Processor utilization = (35 / 35) * 100 = 100 %
Throughput = 4 / 35 = 0.11

23. 2.3.2 Shortest-Process-First (SPF)
Turn around time:
tatA = 35 – 0 = 35
tatB = 31 – 2 = 29
tatC = 17 – 3 =14
tatD = 23 – 7 = 16
tatAVG = ( ) / 4 = 23.5

24. 2.3.2 Shortest-Process-First (SPF)
Turn around time:
tatA = 35 – 0 = 35
tatB = 31 – 2 = 29
tatC = 17 – 3 =14
tatD = 23 – 7 = 16
tatAVG = ( ) / 4 = 23.5

25. 2.3.2 Shortest-Process-First (SPF)
Turn around time:
tatA = 35 – 0 = 35
tatB = 31 – 2 = 29
tatC = 17 – 3 =14
tatD = 23 – 7 = 16
tatAVG = ( ) / 4 = 23.5

26. 2.3.2 Shortest-Process-First (SPF)
Turn around time:
tatA = 35 – 0 = 35
tatB = 31 – 2 = 29
tatC = 17 – 3 =14
tatD = 23 – 7 = 16
tatAVG = ( ) / 4 = 23.5

27. 2.3.2 Shortest-Process-First (SPF)
Turn around time:
tatA = 35 – 0 = 35
tatB = 31 – 2 = 29
tatC = 17 – 3 =14
tatD = 23 – 7 = 16
tatAVG = ( ) / 4 = 23.5

28. 2.3.2 Shortest-Process-First (SPF)
Waiting time:
wtA = (0 – 0) + (18 – 8) + (31 – 26) = 15
wtB = (6 – 2) + (23 – 15) = 12
wtC = (4 – 3) + (15 – 9) = 7
wtD = (14 – 7) + (17 – 16) + (22 – 19) = 11
wtAVG = ( ) / 4 = 11.25

29. 2.3.2 Shortest-Process-First (SPF)
Waiting time:
wtA = (0 – 0) + (18 – 8) + (31 – 26) = 15
wtB = (6 – 2) + (23 – 15) = 12
wtC = (4 – 3) + (15 – 9) = 7
wtD = (14 – 7) + (17 – 16) + (22 – 19) = 11
wtAVG = ( ) / 4 = 11.25

30. 2.3.2 Shortest-Process-First (SPF)
Waiting time:
wtA = (0 – 0) + (18 – 8) + (31 – 26) = 15
wtB = (6 – 2) + (23 – 15) = 12
wtC = (4 – 3) + (15 – 9) = 7
wtD = (14 – 7) + (17 – 16) + (22 – 19) = 11
wtAVG = ( ) / 4 = 11.25

31. 2.3.2 Shortest-Process-First (SPF)
Waiting time:
wtA = (0 – 0) + (18 – 8) + (31 – 26) = 15
wtB = (6 – 2) + (23 – 15) = 12
wtC = (4 – 3) + (15 – 9) = 7
wtD = (14 – 7) + (17 – 16) + (22 – 19) = 11
wtAVG = ( ) / 4 = 11.25

32. 2.3.2 Shortest-Process-First (SPF)
Waiting time:
wtA = (0 – 0) + (18 – 8) + (31 – 26) = 15
wtB = (6 – 2) + (23 – 15) = 12
wtC = (4 – 3) + (15 – 9) = 7
wtD = (14 – 7) + (17 – 16) + (22 – 19) = 11
wtAVG = ( ) / 4 = 11.25

33. 2.3.2 Shortest-Process-First (SPF)
Response time:
rtA = 0 – 0 = 0
rtB = 6 – 2 = 4
rtC = 4 – 3 = 1
rtD = 14 – 7 = 7
rtAVG = ( ) / 4 = 3

34. 2.3.2 Shortest-Process-First (SPF)
Response time:
rtA = 0 – 0 = 0
rtB = 6 – 2 = 4
rtC = 4 – 3 = 1
rtD = 14 – 7 = 7
rtAVG = ( ) / 4 = 3

35. 2.3.2 Shortest-Process-First (SPF)
Response time:
rtA = 0 – 0 = 0
rtB = 6 – 2 = 4
rtC = 4 – 3 = 1
rtD = 14 – 7 = 7
rtAVG = ( ) / 4 = 3

36. 2.3.2 Shortest-Process-First (SPF)
Response time:
rtA = 0 – 0 = 0
rtB = 6 – 2 = 4
rtC = 4 – 3 = 1
rtD = 14 – 7 = 7
rtAVG = ( ) / 4 = 3

37. 2.3.2 Shortest-Process-First (SPF)
Response time:
rtA = 0 – 0 = 0
rtB = 6 – 2 = 4
rtC = 4 – 3 = 1
rtD = 14 – 7 = 7
rtAVG = ( ) / 4 = 3