scheduling调度是什么 优先规则

Posted 2022-03-17 软件工程小施同学

Scheduling

• n jobs 1 machine case
  • Priority rules
  • Comparative measures
• Flow shop case

Scheduling -- determine the timing and order of operations to optimize the use of resources to meet production requirements

n jobs 1 machine case

Priority rules (pg.590)

• First Come First Serve (FCFS)
• Shortest Processing Time (SPT)
• Earliest Due Date (EDD)
• Slack Time Remaining (STR) = time remaining before due date - remaining processing time
•     The shortest STR goes first
• Critical Ratio (CR) = Time remaining before due date/Remaining processing time
•     The smallest CR goes first

 

Comparison of priority rules

Average Completion time/Mean flow time =(Total processing time + total waiting time)/Number of jobs
Average lateness = total late days/number of jobs
 

Example

Given:
 

Job	Processing time (days)	Due Date (days hence)	Slack time remaining	Critical Ratio
A	20	30	10	1.5
B	30	50	20	1.7
C	10	25	15	2.5
D	16	80	64	5.0
E	18	60	42	3.3

 

 

FCFS	Proc. Time	Flow Time	Due Date	Lateness
A	20	20	30	0
B	30	50	50	0
C	10	60	25	35
D	16	76	80	0
E	18	94	60	34
Total	94	300	245	69
Mean		60		13.8

 

SPT	Proc.	Flow	Time to	Lateness
Seq.	Time	Time	Due
C	10	10	25	0
D	16	26	80	0
E	18	44	60	0
A	20	64	30	34
B	30	94	50	44
Total	94	238	245	78
Mean		47.6		15.6

 

SLACK	Proc.	Flow	Time to	Lateness
Seq.	Time	Time	Due
A	20	20	30	0
C	10	30	25	5
B	30	60	50	10
E	18	78	60	18
D	16	94	80	14
Total	94	282	245	47
Mean		56.4		9.4

 

CR	Proc.	Flow	Time to	Lateness
Seq.	Time	Time	Due
A	20	20	30	0
B	30	50	50	0
C	10	60	25	35
E	18	78	60	18
D	16	94	80	14
Total	94	302	245	67
Mean		60.4		13.4

 

EDD	Proc.	Flow	Time to	Lateness
Seq.	Time	Time	Due
C	10	10	25	0
A	20	30	30	0
B	30	60	50	10
E	18	78	60	18
D	16	94	80	14
Total	94	272	245	42
Mean		54.4		8.4

Comparing the priority rules
 
 

Rule	Mean Flow Time	Mean Lateness
FCFS	60	13.8
SPT	**47.6	15.6
STR	56.4	9.4
CR	60.4	13.4
EDD	54.4	**8.4

Exercises

Pg. 607 Problem 5, 13

Flow shop scheduling

n jobs two machines: all jobs require the same sequence/order in visiting the machines

Johnson's rule

If the shortest time is for the first machine, do the job first
If the shortest time is for the second machine, do the job last
 

Example
 
 

Job	Processing Time, M1	Processing Time, M2
A	5	2
B	3	6
C	8	4
D	10	7
E	7	12

Job sequence: B à E à D à C à A

Gantt Chart representation

Exercises

Pg. 606 Problem 3, 9, 12, 14

 

https://www.uky.edu/~dsianita/300/schedule.html#flowshop