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Scheuduling

Scheuduling. Operating System Examples. Solaris scheduling Windows XP scheduling Linux scheduling. Solaris Dispatch Table. Solaris Scheduling. Unix Scheduling. Interactive processes are favored

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Scheuduling

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  1. Scheuduling

  2. Operating System Examples • Solaris scheduling • Windows XP scheduling • Linux scheduling

  3. Solaris Dispatch Table

  4. Solaris Scheduling

  5. Unix Scheduling • Interactive processes are favored - Small CPU time slices are given to processes by a priority algorithm Round Robin for CPU-bound jobs • The more CPU time a process accumulates, the lower its priority becomes (negative feedback) • “Process aging” prevents starvation • Multi-level Feedback Queue with Round Robin within each priority queue • Priority is based on process type and execution history

  6. Windows XP Priorities

  7. Linux Scheduling • Constant order O(1) scheduling time • Two priority ranges: time-sharing and real-time • Real-time range from 0 to 99 and nice value from 100 to 140 • (figure 5.15)

  8. Linux Scheduling • Each process gets a time quantum, based on its priority • - Two arrays of runnable processes, active and expired • - Processes are selected to run from the active array • - When quantum exhausted, process goes on expired • - When active is empty, swap the two arrays

  9. Priorities and Time-slice length

  10. List of Tasks Indexed According to Priorities

  11. Algorithm Evaluation • Deterministic modeling – takes a particular predetermined workload and defines the performance of each algorithm for that workload • Queueing models • Implementation

  12. Evaluation of CPU schedulers by Simulation

  13. Java Thread Scheduling • JVM Uses a Preemptive, Priority-Based Scheduling Algorithm • FIFO Queue is Used if There Are Multiple Threads With the Same Priority

  14. Java Thread Scheduling (cont) JVM Schedules a Thread to Run When: • The Currently Running Thread Exits the Runnable State • A Higher Priority Thread Enters the Runnable State * Note – the JVM Does Not Specify Whether Threads are Time-Sliced or Not

  15. Time-Slicing Since the JVM Doesn’t Ensure Time-Slicing, the yield() Method May Be Used: while (true) { // perform CPU-intensive task . . . Thread.yield(); } This Yields Control to Another Thread of Equal Priority

  16. Thread Priorities PriorityComment Thread.MIN_PRIORITY Minimum Thread Priority Thread.MAX_PRIORITY Maximum Thread Priority Thread.NORM_PRIORITY Default Thread Priority Priorities May Be Set Using setPriority() method: setPriority(Thread.NORM_PRIORITY + 2);

  17. Solaris 2 Scheduling

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