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    SubjectRe: [SCHED] Totally WRONG prority calculation with specific test-case (since 2.6.10-bk12)
    On Wed, 28 Dec 2005 12:35:47 +0100
    Paolo Ornati <ornati@fastwebnet.it> wrote:

    > > This latter thing sounds more like your transcode job pushed everything out to
    > > swap... You need to instrument this case better.
    > >
    >
    > I don't know. The combination Swapped Out Programs + "normal" priority
    > strangeness can potentially result in a total disaster... but why
    > renicing transcode to "0" gets the system usable again?
    >
    > Next time I'll grab "/proc/meminfo"... and what other info can help to
    > understand?

    I'm doing some tests with "ingosched" and a bit longer trancoding
    session and I've found a strange thing.

    DD running time can change a LOT between one run and another (always
    while transcode is running):

    ----------------------------------------------------------------------
    paolo@tux /mnt $ mount space/; sync; sleep 1; time dd if=space/bigfile
    of=/dev/null bs=1M count=256; umount space/ 256+0 records in
    256+0 records out

    real 0m15.754s
    user 0m0.000s
    sys 0m0.500s

    paolo@tux /mnt $ mount space/; sync; sleep 1; time dd if=space/bigfile
    of=/dev/null bs=1M count=256; umount space/ 256+0 records in
    256+0 records out

    real 0m52.966s
    user 0m0.000s
    sys 0m0.504s

    paolo@tux /mnt $ mount space/; sync; sleep 1; time dd if=space/bigfile
    of=/dev/null bs=1M count=256; umount space/ 256+0 records in
    256+0 records out

    real 0m48.928s
    user 0m0.004s
    sys 0m0.524s
    ---------------------------------------------------------------------

    Looking at top while running these I've seen that this is related to
    how transcode's (the one that eats a lot of CPU) priority changes.

    When only transcoding his priority is 16, but when also DD test is
    running then that value fluctuate between 16 and 18.

    DD priority is always 18 instead.

    Usually transcode's prio go to 17/18 and DD runs in 15/20s, but
    sometimes it doesn't fluctuate staying stuck to 16 and DD runs in ~50s.


    PS:
    I'm not yet able to reproduce the "totally unusable system" I was
    talking about.

    --
    Paolo Ornati
    Linux 2.6.15-rc7-plugsched on x86_64
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