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    SubjectRe: low priority soft RT?
    On Wed, Jul 21, 1999 at 09:25:12PM -0500, cd_smith@ou.edu wrote:
    > Anyone thought about allowing soft RT (SCHED_FIFO or SCHED_RR) tasks with
    > negative priorities? These would only be executed if no other tasks of
    > any type are there. Giving a normal Linux task a niceness value won't do
    > this, as the task will still get some CPU time.
    >
    > I was just thinking back to past projects, and about a year ago I wished I
    > had something like this to do background housekeeping tasks for a
    > distributed application I was writing -- I wanted to do them if possible
    > on a free system, and only schedule time on some system if they didn't get
    > scheduled anyway.
    >
    > Since I'm sure this isn't a new idea, any good reasons not to allow this?
    > (surely there can't be security implications, right?) I'm not really
    > interested in doing it myself right now, but I might in the future if
    > there aren't good reasons otherwise.
    >
    > Chris Smith <cd_smith@ou.edu>
    >


    Such a change potentially violates the standard, and at the very least,
    would be non-portable.

    It's also probably a bad idea due to possible priority inversion. A
    better solution might be a process that watches the load average, and if
    it sees that the load is above a certain threshold, say, 0.1, it releases
    all locks and sleeps for a minute. When it wakes, it just repeats the
    check to see if it is OK to run. Put this process at nice -20, and it
    would truly be a no-priority process.

    One caveat is that you need to calculate the load average _minus_ that
    caused by the actual process. Another problem would be if you wanted to
    run multiple no-priority process -- but then, if you care about fairness,
    it's not really no-priority.



    dave...


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