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    SubjectRe: allow non root users to set io priority "idle" ?
    On 06 Aug 2007 13:11:01 +0200, Andi Kleen <andi@firstfloor.org> wrote:
    > For IO I suppose the same could happen too. e.g. low priority
    > task wants to write out a page and keeps it locked until the IO
    > is finished. High priority task wants to access the page and has
    > to wait until it is unlocked. Middle task generates an endless
    > stream of IO that makes the idle priority writeout never finish.

    I don't think it's a problem for high priority (RT) tasks - it's well
    known in the real time Linux community that you never, ever do IO from
    a thread that has to satisfy RT constraints. A correct RT linux app
    does its IO from a SCHED_NORMAL thread, with *plenty* of buffering,
    and feeds the RT constrained SCHED_FIFO threads using a lock free
    ringbuffer.

    SCHED_IDLE starving SCHED_NORMAL is an issue of course. But
    SCHED_IDLE seems a lot more useful for read than write which I would
    expect to take fewer locks. For example I'd expect Beagle to want to
    read at SCHED_IDLE but write out its indices at SCHED_NORMAL.

    Would it make any sense to allow anyone to set SCHED_IDLE for reads
    but require root to change IO priority for writes?

    Lee
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