lkml.org 
[lkml]   [2004]   [Apr]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: PROBLEM: Consistently slower 3ware RAID performance under 2.6.4
    Timothy Miller <miller@techsource.com> wrote:
    >
    > ## Performance with "2.4.25-gentoo":
    >
    > The read test here takes 21.6 seconds which is about 47MB/sec. This is
    > a correct number, because I have measured the maximum read throughput
    > from each drive to be 47MB/sec.
    >
    > The write test here takes 2 minutes, 2.5 seconds. This translates to
    > 8.35MB/sec. This is what I'm working with 3ware to correct, but let's
    > call this the baseline write performance.
    >
    >
    > ## Performance with "2.6.4-gentoo-r1":
    >
    > The read test here takes 33.9 seconds. That's down to about 30MB/sec.
    >
    > The write test here takes 2 minutes, 44.2 seconds. That is down to
    > 6.2MB/sec.
    >

    You cannot compare 2.4 and 2.6 kernel write performance with `dd', because
    the kernels are tuned differently. 2.6 kernels are tuned to leave less
    dirty pages in memory than a 2.4 kernel. Hence when your dd has finished,
    40% of memory will be dirty (needing writeout) under 2.6, but this figure
    is 60% on 2.4.

    So the 2.6 kernel does more writeout during the dd run and less writeout
    after dd has finished. The 2.4 kernel does less writeout during the dd run
    and more writeout after dd has finished.

    To compare IO performance you'll need to set 2.6's /proc/sys/vm/dirty_ratio
    to 60 and /proc/sys/vm/dirty_async_ratio to 30. Or use write-and-fsync
    from http://www.zip.com.au/~akpm/linux/patches/stuff/ext3-tools.tar.gz with
    the `-f' option.

    I don't know why the read bandwidth appears to be lower. Try increasing
    the readahead with `blockdev --setra'?
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 14:02    [W:0.022 / U:0.640 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site