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    Subjectfio sync read 4k block size 35% regression
    Comapraing with 2.6.30, fio sync read (block size 4k) has about 35% regression
    with kernel 2.6.31-rc1 on my stoakley machine with a JBOD (13 SCSI disks).

    Every disk has 1 partition and 4 1-GB files. Start 10 processes per disk to
    do sync read sequentinally.

    Bisected down to below patch.

    51daa88ebd8e0d437289f589af29d4b39379ea76 is first bad commit
    commit 51daa88ebd8e0d437289f589af29d4b39379ea76
    Author: Wu Fengguang <>
    Date: Tue Jun 16 15:31:24 2009 -0700

    readahead: remove sync/async readahead call dependency

    The readahead call scheme is error-prone in that it expects the call sites
    to check for async readahead after doing a sync one. I.e.

    if (!page)
    page = find_get_page();
    if (page && PageReadahead(page))

    I also test block size 64k and 128k, but they don't have regression. Perhaps
    the default read_ahead_kb is equal to 128?

    Other 2 machines have no such regression. The JBODS of the 2 machines consists
    of 12 and 7 SATA/SAS disks while every disk has 2 partitions.

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      Last update: 2009-07-01 05:29    [W:0.037 / U:7.864 seconds]
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