Short Term Scheduling Policies Example 1

1
Short Term Scheduling Policies Example - 1

• Consider a typical Ready queue status of a
  computer system having Uni-processor with support
  for multi programming as given below.
• --------------------------------------------------
  ----------------------------------
• Process Arrival Time Service time
  Deadline Limits
• Chunk No. in units in units
  in units
• --------------------------------------------------
  ----------------------------------
• P0 10 200
  560
• P1 5
  400 1100
• P2 13 250
  none
• P3 8
  50 250
• P4 20 300
  650
• --------------------------------------------------
  -----------------------

2
Short Term Scheduling Policies Example - 2

• Assume Context switching time 1 unit (fixed).
• Dispatcher Execution time 3 units
  (fixed).
• Enqueuer Execution time 2 units
  (fixed).
• For the Ready Queue Status as specified on the
  prev. slide, compare the performances of the
  following non preemptive scheduling policies
• (a)First come First Served (FCFS).
• (b) Shortest Job First (SJF).
• (c) Dead Line based (starting with job having
  shortest service time).

3
Short Term Scheduling Policies Example - 2

• For each of the aforesaid scheduling policies,
  you are to depict the following
• i) Specify the Gantt Chart ( A chart depicting
  the allocation sequence of each process block to
  the CPU as well as the occupancy time.) .
• ii) Compute the average Turn around time.
• iii) Compute the average Waiting time.

4
Short Term Scheduling Policies Example - 3

• Assumption (For all scheduling policies)
• Context Switching Dispatcher Time
• has to be there between any two processes while
  invoking of Enqueuer will also cause the context
  switch before after but there cannot be two
  successive context switches.

Context Switch Dispatcher 1 Unit 3 Units

Context Switch Enqueuer 1 Unit
2 Units
5
Short Term Scheduling Policies Non Pre-emptive
FCFS - 1

• The READY Queue / List structure
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
• --------------------------------------------------
  ------------------------
• P1 5
  400
• P3 8
  50
• P0 10 200
  
• P2 13 250
  
• P4 20 300
  
• --------------------------------------------------
  ------------------------

6
Short Term Scheduling Policies Non Pre-emptive
FCFS - 2

• GANTT Chart

P1
P3
P0
P2
P4
DiS
DiS
DiS
DiS
DiS P1
EnQ P1
EnQ P3
EnQ P0
EnQ P2
EnQ P4
5 8 11 14 17 22 25
425 430 480 485
685 690 940 945 1245

7
Short Term Scheduling Policies Non Pre-emptive
FCFS - 3

• The Various Time Structure
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
  Turnaround Waiting
• 
  Time Time
• --------------------------------------------------
  ------------------------
• P1 5
  400 425- 5 420 25-5
  20
• P3 8
  50 480-8 472 430-8 422
  
• P0 10 200
  685-10 675 485-10 475
• P2 13 250
  940-13927 690-13 677
• P4 20 300
  1245-201225 945-20 925
• --------------------------------------------------
  ---------------------------------------

8
Short Term Scheduling Policies Non Pre-emptive
FCFS - 4

• Total Turn Around Time 4204726759271225
  3719 units
• Average Turn Around Time 3719 / 5 743.8
  units
• Total Waiting Time 20422475677925 2519
  units
• Average Waiting Time 2519 / 5 503.8 units

9
Short Term Scheduling Policies Non Pre_emptive
SJF - 1

• Ready List / Queue Structure
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
  Deadline Limits
• No. in units in units
  in units
• --------------------------------------------------
  ------------------------
• P3 8
  50 250
• P0 10 200
  560
• P2 13 250
  none
• P4 20 300
  650
• P1 5
  400 1100
• --------------------------------------------------
  ------------------------

10
Short Term Scheduling Policies Non Pre-emptive
SJF - 2

• GANTT Chart

P3
P0
P2
P4
P1
DiS
DiS
DiS
DiS
DiS P3
EnQ P1
EnQ P3
EnQ P0
EnQ P2
EnQ P4
5 8 11 14 17 22 25
75 80 280 285
535 540 840 845
1245
11
Short Term Scheduling Policies Non Pre-emptive
SJF - 3

• The various Time Status
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
  Turnaround Waiting
• 
  Time Time
• --------------------------------------------------
  ------------------------
• P3 8
  50 75-8 67 25-8 17
• P0 10 200
  280-10 270 80-10 70
• P2 13 250
  535-13522 285-13 272
• P4 20 300
  840-20820 540-20 520
• P1 5
  400 1245- 5 1240 845-5 840
  
• --------------------------------------------------
  ---------------------------------------

12
Short Term Scheduling Policies Non Pre-emptive
SJF - 4

• Total Turn Around Time 672705228201240
  2919 units
• Average Turn Around Time 2919/ 5 583.8
  units
• Total Waiting Time 1770272520840 1719
  units
• Average Waiting Time 1719 / 5 343.8 units

13
Short Term Scheduling Policies Non Pre-emptive
Deadline Based - 1

• Ready List/ Queue Structure
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
  Deadline Limits
• No. in units in units
  in units
• --------------------------------------------------
  ------------------------
• P3 8
  50 250
• P0 10 200
  560
• P4 20 300
  650
• P1 5
  400 1100
• P2 13 250
  none
• --------------------------------------------------
  ------------------------

14
Short Term Scheduling Policies Non Pre-emptive
Deadline Based - 2

• GANTT Chart

P3
P0
P4
P1
P2
DiS
DiS
DiS
DiS
DiS P3
EnQ P1
EnQ P3
EnQ P0
EnQ P2
EnQ P4
5 8 11 14 17 22 25
75 80 280 285
585 590 990 945
1195
15
Short Term Scheduling Policies Non Pre-emptive
Deadline Based - 3

• The various Time Status
• --------------------------------------------------
  ------------------------
• Process Arrival Time Service time
  Turnaround Waiting
• 
  Time Time
• --------------------------------------------------
  ------------------------
• P3 8
  50 75-8 67 25-8 17
• P0 10 200
  280-10 270 80-10 70
• P4 20 300
  585-20565 285-20 265
• P1 5
  400 990- 5 985 590-5 585
  
• P2 13 250
  1195-131182 945-13932
• --------------------------------------------------
  ---------------------------------------

16
Short Term Scheduling Policies Non Pre-emptive
Deadline Based - 4

• Total Turn Around Time 672705659851182
  3069 units
• Average Turn Around Time 3069 / 5 613.8
  units
• Total Waiting Time 1770265585 932 1869
  units
• Average Waiting Time 1869 / 5 373.8 units