[lkml]   [2006]   [Aug]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: Accuracy of disk statistics IO counter
    On Tue, Aug 01 2006, Mark Seger wrote:
    > >>Specifically, I wrote a 1GB file with a blocksize of 1MB, which would
    > >>result in 1000 writes at the application level. What I believe then
    > >>happens is that each write turns into 8 128KB requests to the driver,
    > >>which should result in 8000 actual writes. Toss in metadata operations
    > >>and who knows what else and the actual number should be a little
    > >>higher. What I've see after repeating the tests a number of times on
    > >>2.6.16-27 is numbers ranging from 6800-7000 writes which feels like a
    > >>big enough difference to at least point out.
    > >>
    > >>
    > >
    > >Install
    > >and blktrace your disk for the duration of the test and compare the io
    > >numbers. Requires 2.6.17 or later, though.
    > >
    > >
    > I had problems getting blktrace going and posted a note to
    > at Alan Brunelle's suggestion and he also

    Documentation issues, sorry about that. It hasn't been updated for the
    debugfs change.

    > said he'd take a closer look at it himself. On the other hand he
    > pointed me to 'stap' and I was able to use it to get the details I was
    > looking for - SystemTAP really rocks for this type of analysis! As it
    > turns out my assumption about driver blocksize was wrong (sorry about
    > that). It turns out that the size of requests from the driver to the
    > disk is 160mb and so the I/O count was smaller than I had anticipated.

    160KiB, I'm assuming? :-)

    Jens Axboe

    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2006-08-01 21:41    [W:0.021 / U:6.968 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site