lkml.org 
[lkml]   [2006]   [Dec]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Linux disk performance.
    On 12/21/06, Bill Davidsen <davidsen@tmr.com> wrote:
    > >
    > > But isn't O_DIRECT supposed to bypass buffering in Kernel?
    > That's correct. But it doesn't put your write at the head of any queue,
    > it just doesn't buffer it for you.
    >
    > > Doesn't it directly write to disk?
    > Also correct, when it's your turn to write to disk...

    But the only process accessing that disk is my application.

    > > I tried to put fdatasync() at regular intervals but there was no
    > > visible effect.
    > >
    > Quite honestly, the main place I have found O_DIRECT useful is in
    > keeping programs doing large i/o quantities from blowing the buffers and
    > making the other applications run like crap. If you application is
    > running alone, unless you are very short of CPU or memory avoiding the
    > copy to an o/s buffer will be down in the measurement noise.

    Yes... my application does large amount of I/O. It actually writes
    video data received from ethernet(IP camera) to the disk using 128 K
    chunks.

    > I had a news (usenet) server which normally did 120 art/sec (~480 tps),
    > which dropped to about 50 tps when doing large file copies even at low
    > priority. By using O_DIRECT the impact essentially vanished, at the cost
    > of the copy running about 10-15% slower. Changing various programs to
    > use O_DIRECT only helped when really large blocks of data were involved,
    > and only when i/o clould be done in a way to satisfy the alignment and
    > size requirements of O_DIRECT.
    >
    > If you upgrade to a newer kernel you can try other i/o scheduler
    > options, default cfq or even deadline might be helpful.

    I tried all disk schedulers but all had timing bumps. :(

    > --
    > bill davidsen <davidsen@tmr.com>
    > CTO TMR Associates, Inc
    > Doing interesting things with small computers since 1979
    >


    --
    ---------------------------------------------------------------
    regards
    Manish Regmi

    ---------------------------------------------------------------
    UNIX without a C Compiler is like eating Spaghetti with your mouth
    sewn shut. It just doesn't make sense.
    -
    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: 2006-12-21 07:07    [W:0.024 / U:32.940 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site