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    SubjectRe: AIO!!
    Date
    On Tuesday 11 October 2005 08:04, Karthik Sarangan wrote:
    > > Benjamin LaHaise wrote:
    > > O_DIRECT buffers must be aligned on block sized boundaries (minimum 512
    > > bytes). Check the actual return code from the aiocb and you'll find that
    > > it is likely -EINVAL, no -EINPROGRESS. See the man page for
    > > posix_memalign() to properly align the pointer.
    >
    > EEP!! I forgot all about buffer alignment!! Thanks for pointing it out

    Why do you constantly shout?

    > ------------------
    > Two more questions.
    >
    > 1. Is aio_fsync of any use while 'aio_read'ing and 'aio_write'ing to
    > a 'raw' device or a '/dev/sdb' with O_DIRECT?

    I suspect you did not do some research first.

    > 2. I have an Ultra320 SCSI disk whose datasheet says it has a max.
    > possible throughput of 78MBps
    >
    > I did a 'aio_write' onto '/dev/sdb' with O_DIRECT.
    > Following are some throughput values.
    >
    > Buffer for IO | Avg Speed
    > (in KBytes) |
    > ----------------O-----------
    > Upto 512KB | 69MBps
    > 1024KB | 125MBps
    > 2048KB | 250MBps
    > 4096KB | 500MBps
    > 8192KB | 1GBps -- What the !! --

    Most probably bug in your program.

    > Buffer cache does not come into consideration.
    >
    > Does this mean that the SCSI lower layer (aic79xx) can transfer data
    > only upto 512 KB?

    It means that you are in dire need of reading this:

    http://www.catb.org/~esr/faqs/smart-questions.html

    --
    vda
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