Queues when accessing disks

From: Felipe Erias (charles.swann_at_gmail.com)
Date: 12/31/04

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    Date:	Fri, 31 Dec 2004 04:32:59 +0100
To: linux-kernel@vger.kernel.org

    Hi,

    I'm trying to apply queuing theory to the study of the GNU/Linux kernel.
    Right now, I'm focusing in the queue of processes that appears when they
    try to access an I/O device (specifically, an IDE HD). When they want to
    read data, it behaves as a usual queue: several clients (processes) that
    require attention from a server (disk / driver / ...). The case when they want
    to write data is a bit more tricky, because of the cache buffers used by the OS,
    and maybe could be modelized by a network of queues. Both cases are
    interesting for my work, but I'll take the reading one first, just
    because it seems
    a bit more simple 'a priori'.

    To modelize the queue, I need to get some information:
     - what processes claim attention from the disk
     - when they do it
     - when they begin to be served
     - when they finish being served

    To get all this information, maybe I could hack my kernel a bit to write
    a line to a log on every access to the HD, or account the IRQs from
    the IDE channels... I also have the feeling that this queuing problem could
    dissappear o became more hidden if DMA were enabled.

    To be true, I'm a bit lost and that's why I ask for your help.

    Yours sincerely,

      Felipe Erias
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