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    SubjectRe: periods and deadlines in SCHED_DEADLINE
    On Fri, 2010-07-09 at 16:32 +0200, Peter Zijlstra wrote:
    > On Fri, 2010-07-09 at 15:38 +0200, Raistlin wrote:
    > > - do you think it could be useful to have a different syscall to deal
    > > with the period parameter (if it's different from deadline), e.g.,
    > > something useful to make the task periodic as you have (if I remember
    > > well) in Xenomai or RTAI?
    > > If you think it's worth doing that, do you think the
    > > task_wait_interval() syscall that we already added could/should do
    > > the job?
    > Again, I'm afraid I need some extra education here in order to make a
    > sensible comment.
    Hey, fine, where's the problem? :-P

    > What are the exact semantics of this extra proposed syscall?
    Right now, it is:
    task_wait_interval(t) --> "wake me up at the first instant after t when
    you can give me my full runtime"

    > What exactly are the benefits over not having it, and simply rely on the
    > task to not wake up more often, but if it does have it run into the lack
    > of budget and sort it that way?
    What you're saying obviously will always work, and it is actually a
    quite common usage pattern (we use it like that a lot! :-)).

    The new syscall might help when it is important for a task to
    synchronize with the budget provisioning mechanism. It might be
    uncommon, but there could be situations --more in hard than in soft
    scenarios-- where you want to be sure that you're next job (and all the
    subsequent ones, if you behave well) will get its full runtime, even if
    this means waiting a little bit.

    what I was wondering was if this semantic should be modified by the
    introduction of the "period", but I also agree with Luca that we must do
    our best to avoid confusion!

    <<This happens because I choose it to happen!>> (Raistlin Majere)
    Dario Faggioli, ReTiS Lab, Scuola Superiore Sant'Anna, Pisa (Italy) / /
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      Last update: 2010-07-10 09:53    [W:0.039 / U:144.568 seconds]
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