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    SubjectRe: Real Time Runqueue
    On Fri, Nov 16, 2001 at 02:44:30PM -0800, Davide Libenzi wrote:
    >
    > I do not use a separate queue coz, if it's single, it becomes a common
    > lock for all CPUs.
    > RT tasks are scheduled as usual and the only problem arises in
    > reschedule_idle() when an RT task is pushed onto the run queue when
    > 1) on its CPU it is _not_ running the idle
    > 2) on its CPU is running another RT task with higher priority
    >
    > In that case a "good CPU" discovery loop is triggered, the task is moved
    > on that CPU runqueue, need_resched is set, an IPI is sent and on return
    > from the remote CPU IPI path the RT task is run.
    > A good solution would be ( i'm not doing it now ), in setscheduler() to
    > move the task in a way to have an even distribution of RT tasks among
    > CPUs.
    >
    > - Davide

    Davide,

    Suppose you have a 2 CPU system with 4 runnable tasks. 3 of these
    tasks are realtime with the same realtime priority and the other is
    an ordinary SCHED_OTHER task. The task distribution on the runqueues
    looks something like this.

    CPU 0 CPU 1
    --------- ---------
    RT Task A RT Task B
    Other Task C RT Task D

    Task A and Task B are currently running on the 2 CPUs. Now, Task A
    voluntarily gives up CPU 0 and Task B is still running on CPU 1.
    At this point, Task D should be chosen to run on CPU 0. Correct?
    Isn't this a required RT semantic? I'm curious how you plan on
    accomplishing this.

    Regards,
    --
    Mike
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