Optimization criteria turnaround time is not a good

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Optimization Criteria Turnaround Time is not a good criteria for Interactive Systems A process may Produce “Some” output Computes new results, while previous results are output to the user Response Time Response_Time = First_Response_Start_Time Submission_Time
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14 Optimization Criteria - Summary Optimization Criteria - Summary We would like to Maximize CPU Utilization Throughput And Minimize Turnaround Time Waiting Time Response Time
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15 Scheduling Algorithms Scheduling Algorithms First come, First serve Shortest Job First Priority Scheduling Round-Robin Scheduling Multi-level Queue Scheduling Multi-level Feed back queue Scheduling
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16 First come, First serve First come, First serve Simplest scheduling algorithm: Run jobs in order that they arrive Uni-programming: Run until done Multi-programming: Run until done or Blocks on I/O Nonpreemptive A Process keeps CPU until done or I/O Advantage: Simplicity
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17 First come, First serve First come, First serve Disadvantage Wait time depends on arrival order Unfair to later jobs (worst case: long job arrives first) Three jobs (times: A=100, B=1, C=2) arrive in the order A, B, C time 100 101 103 cpu A B C Average Waiting Time = (0 + 100 + 101) / 3 = 67
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18 First come, First serve First come, First serve Average Waiting Time = (0 + 1 + 3) / 3 = 1.33 Now if they arrive in the order B, C, A cpu time 1 3 103 A B C
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19 FCFS Convoy effect FCFS Convoy effect A CPU bound job will hold CPU until Terminates Or it causes an I/O burst Rare occurrence, since the thread is CPU-bound Long periods where no I/O requests issued, and CPU held Result: Poor I/O device utilization
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20 FCFS Convoy effect : Example Example
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