CHAPTER 2 PROCESSOR SCHEDULING PART II

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CHAPTER 2PROCESSOR SCHEDULINGPART II

• by Ugur HALICI

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2.5 Processor Scheduling algorithms

• The goal of a scheduling algorithm is to select
  the most appropriate process in the ready queue.
• For simplicity, we will assume that
• we have a single I/O server and a single device
  queue,
• device queue always implemented with FCFS (FIFO)
  method.
• We also will neglect the switching time between
  processes (context switching).

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2.5 Processor Scheduling algorithms

• We will consider the following processes and will
  apply different scheduling algorithms on it.

Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
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2.3.1 First-Come-First-Served (FCFS)

• In this algorithm, the process to be selected is
  the process which requests the processor first.
• This is the process whose PCB is at the head of
  the ready queue.
• Contrary to its simplicity, its performance may
  often be poor compared to other algorithms.

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2.3.1 First-Come-First-Served (FCFS)

• FCFS may cause processes with short processor
  bursts to wait for a long time.
• If one process with a long processor burst gets
  the processor, all the others will wait for it to
  release it and the ready queue will be crowded.
• This is called the convoy effect.

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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ B
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ B C
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ B C
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ C D
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ C D A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ C D A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ D A B
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ D A B
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ A B C
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ B C D
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ B C D
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ C D A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ C D A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ D A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ A
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ D
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ D
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2.3.1 First-Come-First-Served (FCFS)
Process Arrival time 1st exec 1st I/O 2nd exec 2nd I/O 3rd exec
A 0 4 4 4 4 4
B 2 8 1 8 - -
C 3 2 1 2 - -
D 7 1 1 1 1 1
RQ
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2.3.1 First-Come-First-Served (FCFS)

• Processor utilization (35 / 35) 100 100
• Throughput 4 / 350.11

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2.3.1 First-Come-First-Served (FCFS)

• Turn around time
• tatA 34 0 34
• tatB 27 2 25
• tatC 29 3 26
• tatD 35 7 28 
• tatAVG (34 25 26 28) / 4 28.25

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2.3.1 First-Come-First-Served (FCFS)

• Turn around time
• tatA 34 0 34
• tatB 27 2 25
• tatC 29 3 26
• tatD 35 7 28 
• tatAVG (34 25 26 28) / 4 28.25

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2.3.1 First-Come-First-Served (FCFS)

• Turn around time
• tatA 34 0 34
• tatB 27 2 25
• tatC 29 3 26
• tatD 35 7 28 
• tatAVG (34 25 26 28) / 4 28.25

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2.3.1 First-Come-First-Served (FCFS)

• Turn around time
• tatA 34 0 34
• tatB 27 2 25
• tatC 29 3 26
• tatD 35 7 28 
• tatAVG (34 25 26 28) / 4 28.25

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2.3.1 First-Come-First-Served (FCFS)

• Turn around time
• tatA 34 0 34
• tatB 27 2 25
• tatC 29 3 26
• tatD 35 7 28 
• tatAVG (34 25 26 28) / 4 28.25

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2.3.1 First-Come-First-Served (FCFS)

• Waiting time
• wtA (0 0) (15 8) (30 23) 14
• wtB (4 2) (19 13) 8
• wtC (12 3) (27 15) 21
• wtD (14 7) (29 16) (34 31) 23
•  
• wtAVG (14 12 21 23) / 4 16.5

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2.3.1 First-Come-First-Served (FCFS)

• Waiting time
• wtA (0 0) (15 8) (30 23) 14
• wtB (4 2) (19 13) 8
• wtC (12 3) (27 15) 21
• wtD (14 7) (29 16) (34 31) 23
•  
• wtAVG (14 12 21 23) / 4 16.5

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2.3.1 First-Come-First-Served (FCFS)

• Waiting time
• wtA (0 0) (15 8) (30 23) 14
• wtB (4 2) (19 13) 8
• wtC (12 3) (27 15) 21
• wtD (14 7) (29 16) (34 31) 23
•  
• wtAVG (14 12 21 23) / 4 16.5

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2.3.1 First-Come-First-Served (FCFS)

• Waiting time
• wtA (0 0) (15 8) (30 23) 14
• wtB (4 2) (19 13) 8
• wtC (12 3) (27 15) 21
• wtD (14 7) (29 16) (34 31) 23
•  
• wtAVG (14 12 21 23) / 4 16.5

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2.3.1 First-Come-First-Served (FCFS)

• Waiting time
• wtA (0 0) (15 8) (30 23) 14
• wtB (4 2) (19 13) 8
• wtC (12 3) (27 15) 21
• wtD (14 7) (29 16) (34 31) 23
•  
• wtAVG (14 12 21 23) / 4 16.5

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2.3.1 First-Come-First-Served (FCFS)

• Response time
• rtA 0 0 0
• rtB 4 2 2
• rtC 12 3 9
• rtD 14 7 7
• rtAVG (0 2 9 7) / 4 4.5

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2.3.1 First-Come-First-Served (FCFS)

• Response time
• rtA 0 0 0
• rtB 4 2 2
• rtC 12 3 9
• rtD 14 7 7
• rtAVG (0 2 9 7) / 4 4.5

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2.3.1 First-Come-First-Served (FCFS)

• Response time
• rtA 0 0 0
• rtB 4 2 2
• rtC 12 3 9
• rtD 14 7 7
• rtAVG (0 2 9 7) / 4 4.5

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2.3.1 First-Come-First-Served (FCFS)

• Response time
• rtA 0 0 0
• rtB 4 2 2
• rtC 12 3 9
• rtD 14 7 7
• rtAVG (0 2 9 7) / 4 4.5

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2.3.1 First-Come-First-Served (FCFS)

• Response time
• rtA 0 0 0
• rtB 4 2 2
• rtC 12 3 9
• rtD 14 7 7
• rtAVG (0 2 9 7) / 4 4.5