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CS1550 Recitation

CS1550 Recitation. Mengmeng Li LMM@cs.pitt.edu Office hours: Wed 2:15-4:45pm, Fri 3:00-4:00pm Office: Sennot Square 6805. goal. Review the CPU scheduling. Exercises. Project 1. motivation.

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CS1550 Recitation

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  1. CS1550 Recitation Mengmeng Li LMM@cs.pitt.edu Office hours: Wed 2:15-4:45pm, Fri 3:00-4:00pm Office: Sennot Square 6805

  2. goal • Review the CPU scheduling. • Exercises. • Project 1.

  3. motivation • When a computer is multiprogrammed, it frequently has multiple processes or threads competing at the same time. • If only one CPU is available, a choice has to be made which process to run next. • Scheduler: The part of the OS that makes the choice. • Scheduling algorithm:

  4. categories • Preemptive algorithm • Nonpreemptive algorithm

  5. definitions • Throughput: The number of jobs per hour that the system completes • Turnaround time: the statistically average time from the moment that a batch job is submitted until the moment it is completed.

  6. Scheduling in batch systems • First-come first-served Non-preemptive • Shortest job first Non-preemptive • Round Robin Preemptive

  7. First-come first-served • Example 1: Throughput = 60*3/(24+3+3) = 6 Turnaround time = (24 + 26 +28)/3 = 26

  8. First-come first-served • Exercise 1

  9. First-come first-served • Exercise 2

  10. Shortest job first • Example 1: P1 P4 P2 P3 Throughput = 60*4/(10+8+18+3) = 6 Turnaround time = (10 + 3+ 19 + 33)/4 = 17.5

  11. Shortest job first • Exercise 1

  12. Shortest job first • Example 2:

  13. Round Robin • Example Time quantum: 5 • Throughput = 60*4/(10+8+18+3) = 6 • Turnaround = (23+24+33+8)/4 = 22 P1(5) P2(5) P3(5) P4(3) P1(5) P2(3) P3(13)

  14. Round Robin • Exercise

  15. Project 1 • Run the skeleton programs.

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