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Thread: static vs dynamic scheduling

  1. #1
    Join Date
    Feb 2008
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    Ubuntu 10.04 Lucid Lynx

    static vs dynamic scheduling

    in my OS class we were covering scheduling (just skimmed over the topic) but professor really never really explained the difference between static and dynamic scheduling? all i know is that static means that nothing changes, and dynamic means that something changes. i'd appreciate the if anyone could explain what those "nothing" and "something" mean.

    thanks

  2. #2
    Join Date
    Oct 2007
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    Lubuntu 12.10 Quantal Quetzal

    Re: static vs dynamic scheduling

    Indeed, the question you are asking is not answered in the "scheduling (computing)" wikipedia article. So I'll try that here, as the question doesn't seem to be precisely homework:

    A static schedule is some kind of list containing the order of the processes and the durations in which they are scheduled. For example, a simple communicating device could have the following static schedule in pseudo-code:
    Code:
    repeat forever:
       execute task 1 for 10 ms
       execute task 2 for 20 ms
       execute task 1 for 5 ms
       execute task 3 for 15 ms
    This is a static schedule. It's just like the bus schedule: Task three is executed for 15 ms every 50 ms. The schedule never changes, even if task 1 has nothing to do and task 2 is missing its deadlines.

    On the other hand, when performing dynamic scheduling, whenever the scheduler decides which task to execute next (and for how long), it looks at a list of tasks requesting the processor at that point in time and then decides which to use next. Examples are the "earliest-deadline first" scheduler. Here, the schedule changes if some task has nothing to do and does not request resources.

    There are a couple of books on embedded systems where you can read more about that.

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