lkml.org 
[lkml]   [2012]   [Apr]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: dramatic I/O slowdown after upgrading 2.6.38->3.0+
    On 10.04.2012 06:26, Dave Chinner wrote:

    > Barriers. Turn them off, and see if that fixes your problem.

    Thank you Dave for a hint. And nope, that's not it, not at all... ;)
    While turning off barriers helps a tiny bit, to gain a few %% from
    the huge slowdown, it does not cure the issue.

    Meanwhile, I observed the following:

    1) the issue persists on more recent kernels too, I tried 3.3
    and it is also as slow as 3.0.

    2) at least 2.6.38 kernel works fine, as fast as 2.6.32, I'll
    try 2.6.39 next.

    I updated $subject accordingly.

    3) the most important thing I think: this is general I/O speed
    issue. Here's why:

    2.6.38:
    # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100
    100+0 records in
    100+0 records out
    104857600 bytes (105 MB) copied, 1.73126 s, 60.6 MB/s

    3.0:
    # dd if=/dev/sdb of=/dev/null bs=1M iflag=direct count=100
    100+0 records in
    100+0 records out
    104857600 bytes (105 MB) copied, 29.4508 s, 3.6 MB/s

    That's about 20 times difference on direct read from the
    same - idle - device!!

    Preparing for another bisect attempt, slowly.....

    Thank you!

    /mjt


    \
     
     \ /
      Last update: 2012-04-10 08:03    [W:0.021 / U:30.524 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site