Queues when accessing disks

[Felipe Erias]

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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