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    SubjectRe: patch] Real-Time Preemption, plist fixes
    On Sun, 5 Jun 2005, Ingo Molnar wrote:

    >
    > * Esben Nielsen <simlo@phys.au.dk> wrote:
    >
    > > When K is a constant or bounded by a constant (140 in this
    > > application) any function which is O(K) is O(1) per definition of O!
    >
    > technically you are right. But the question is - while K is considered a
    > constant, and N (nr_running_RT_tasks) is technically not bounded - in
    > practice N is bounded just as much. Have you ever seen any hard-RT
    > application that has more than 140 threads _running at the same time_ on
    > a single CPU? You can even enforce it to be theoretically bounded, via
    > ulimits.
    >
    > in fact, K and N should be pretty close to each other for most
    > applications. I'd be interested in real application scenarios where N is
    > much (== more than 10 times) larger than K and plists really matter.
    >

    I think that would only be the case when an application has an error. The
    problem now is: Say you have two RT applications running, one living
    in priority 0-49 and one in 50-99. Let us say the second has such an
    error, like keep spawning threads whichs blocks on a mutex owned by a task
    which is blocked forever. Without plists such an error will kill the high
    priority RT task. With plists it will only see a _limited_ effect on it's
    latency.

    You can say plists is better at isolating applications wrt. timing than
    ordinary sorted lists.

    > Ingo
    >

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