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    SubjectPROBLEM: Heavy iowait on 2.6 kernels
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    I recently discovered why my new Gentoo server slows to a crawl on a
    intermediate load on the 2.6 kernel series. The reason seems to be an
    unusual amount of iowait.
    I can reproduce this on two systems, one with a KT400 and and one with
    Sis735 chipset.

    iostat -c 1 (or vmstat) while running something like bonnie produces
    iowaits of 99%.
    Any 2.6 kernel responds the same (regardless of the patchset), even
    vanilla. (2.6.5-mm, 2.6.6-mm, 2.6.6-vanilla and 2.6.5-gentoo-r1).
    Any 2.4-series kernel is fine.

    This is a sample iostat output
    --
    avg-cpu: %user %nice %sys %iowait %idle
    26.73 0.00 10.89 62.38 0.00
    avg-cpu: %user %nice %sys %iowait %idle
    0.00 0.00 13.00 87.00 0.00
    avg-cpu: %user %nice %sys %iowait %idle
    1.01 0.00 16.16 82.83 0.00
    avg-cpu: %user %nice %sys %iowait %idle
    0.00 0.00 11.88 88.12 0.00
    avg-cpu: %user %nice %sys %iowait %idle
    0.00 0.00 1.01 98.99 0.00
    avg-cpu: %user %nice %sys %iowait %idle
    0.99 0.00 2.97 96.04 0.00
    --
    --
    ______________________________________________________________________

    Guy Van Sanden
    http://unixmafia.port5.com

    Registered Linux user #249404 - September 1997
    ______________________________________________________________________

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