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    SubjectRe: periods and deadlines in SCHED_DEADLINE
    On Sat, 2010-07-10 at 09:11 +0200, Luca Abeni wrote:
    > On Fri, 2010-07-09 at 16:24 +0200, Peter Zijlstra wrote:
    > > On Fri, 2010-07-09 at 15:38 +0200, Raistlin wrote:
    > > > Basically, from the scheduling point of view, what it could happen is
    > > > that I'm still _NOT_ going to allow a task with runtime Q_i, deadline
    > > > D_i and period P_i to use more bandwidth than Q_i/P_i, I'm still using D
    > > > for scheduling but the passing of the simple in-kernel admission test
    > > > Sum_i(Q_i/P_i)<1 won't guarantee that the task will always finish its
    > > > jobs before D.
    > >
    > > But the tardiness would still be bounded, right? So its a valid Soft-RT
    > > model?

    > I think that if Sum_i(Q_i/P_i)<1 but Sum_i(Q_i/min{P_i,D_i})>=1 then you
    > can have sporadic deadline misses, but it should still be possible to
    > compute an upper bound for the tardiness.
    > But this is just a feeling, I have no proof... :)

    The paper referenced by Bjoern yesterday mentioned that Baruah et al.
    did that proof.

    "For the considered case di < pi , Baruah et al. [7] showed
    that the complexity increases considerably. However, as-
    suming the processor utilization to be strictly less than 1,
    Baruah et al. [6, 7] proved that if a deadline is missed,
    this happens within a maximum time upper bound which
    can be computed."

    [6] S. Baruah, A. Mok, and L. Rosier. Preemptively scheduling
    hard-real-time sporadic tasks on one processor. Proceedings
    of the 11th IEEE Real-Time Systems Symposium, December 1990.

    [7] S. Baruah, L. Rosier, and R. Howell. Algorithms and
    complexity concerning the preemptive scheduling of peri-
    odic real-time tasks on one processor. Real-Time Systems,
    2(4):301–324, November 1990.

    It also jives well with that I remember from reading through Jim's
    papers on Soft-RT G-EDF.
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