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    SubjectRe: [RFC][PATCH 18/22] sched: add reclaiming logic to -deadline tasks
    On 12/11/10 18:51, Peter Zijlstra wrote:
    > On Fri, 2010-11-12 at 18:41 +0100, Luca Abeni wrote:
    >>> The problem the stochastic execution time model tries to address is the
    >>> WCET computation mess, WCET computation is hard and often overly
    >>> pessimistic, resulting in under-utilized systems.
    >> [...]
    >> BTW, sorry for the shameless plug, but even with the current
    >> SCHED_DEADLINE you are not forced to dimension the runtime using the
    >> WCET.
    > Yes you are, it pushes the deadline back on overrun.
    I think in case of overrun it postpones the deadline (by a period P),
    avoiding to execute the task until the end of the current period, right?

    > The idea it to
    > maintain the deadline despite overrunning your budget (up to a point).
    > The paper we're all talking about is:
    > A. Mills and J. Anderson, " A Stochastic Framework for Multiprocessor
    > Soft Real-Time Scheduling", Proceedings of the 16th IEEE Real-Time and
    > Embedded Technology and Applications Symposium, pp. 311-320, April 2010.
    I see... This is a different approach to stochastic analysis, which
    requires modifications to the scheduler.

    In the analysis I mentioned, you still enforce a maximum runtime C every
    period P, but C can be smaller than the WCET of the task. If C is larger
    than the average execution time, you can use queuing theory to find the
    probability to miss a deadline (or, the probability to finish a job in a
    time x * P).


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