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Process Scheduling ( 5.1-5.3)

Process Scheduling ( 5.1-5.3). CPE 261403 - Operating Systems http:// www.e-cpe.org/moodle. The Assumption that Makes Multiprogramming Work. CPU-Bound Process I/O-Bound Process. Figure 5.1. Process Scheduling. Figure 3.6. Scheduling Circumstances (5.1.3). Figure 3.2. Scheduling Modes.

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Process Scheduling ( 5.1-5.3)

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  1. Process Scheduling(5.1-5.3) CPE 261403 - Operating Systems http://www.e-cpe.org/moodle

  2. The Assumption that Makes Multiprogramming Work • CPU-Bound Process • I/O-Bound Process Figure 5.1

  3. Process Scheduling Figure 3.6

  4. Scheduling Circumstances (5.1.3) Figure 3.2

  5. Scheduling Modes Non-Preemptive A A A B B B B A A A Preemptive A A B B A

  6. Scheduling Modes: Nonpreemptive (Cooperative)

  7. Scheduling Modes: Preemptive

  8. Ever seen Windows 1.0?

  9. The very first Mac OS (1984)

  10. Scheduling Criteria (5.2) • CPU Utilization (Percent) • Throughput (Processes per time unit) • Turnaround time (time units) • Waiting time (time units) • Response time (time units)

  11. Scheduling Algorithms (5.3)

  12. P1 P2 P3 0 24 27 30 First-Come, First-Serve (FCFS) ProcessBurst Time P1 24 P2 3 P3 3 • Waiting time for P1 = 0; P2 = 24; P3 = 27 • Average waiting time: (0 + 24 + 27)/3 = 17

  13. P2 P3 P1 0 3 6 30 First-Come, First-Serve (FCFS) • P2, P3, P1 Waiting time for P1 = 6; P2 = 0; P3 = 3 Average waiting time: (6 + 0 + 3)/3 = 3

  14. Shortest-Job-First Scheduling (SJF) • SJF is optimal – gives minimum average waiting time • Two schemes: • Nonpreemptive • Preemptive (shortest-remaining-time-first)

  15. Predicting CPU Burst Time Exponential Average

  16. Prediction Example Actual Prediction Figure 5.3

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