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    SubjectRe: [PATCH] cfq + io priorities
    Jens Axboe writes:
    > On Sun, Nov 09 2003, Guillaume Chazarain wrote:

    >> A process has an assigned io nice level, anywhere
    >> from 0 to 20. Both of
    >> OK, I ask THE question : why not using the normal
    >> nice level, via current->static_prio ? This way,
    >> cdrecord would be RT even in IO, and nice -19
    >> updatedb would have a minimal impact on the system.
    > I don't want to tie io prioritites to cpu
    > priorities, that's a design decision.

    Sure, but do it in a way that's friendly to
    all the apps and admins that only know "nice".

    nice_cpu sets CPU niceness
    nice_net sets net niceness
    nice_disk sets disk niceness
    nice sets all niceness values at once

    >>> these end values are "special" - 0 means the process
    >>> is only allowed to do io if the disk is idle, and 20
    >>> means the process io is considered
    >> So a process with ioprio == 0 can be forever
    >> starved. As it's not
    > Yes
    >> done this way for nice -19 tasks (unlike FreeBSD),
    >> wouldn't it be safer to give a very long deadline
    >> to ioprio == 0 requests ?
    > ioprio == 0 means idle IO. It follows from that that
    > you can risk infinite starvation if other io is happening.
    > Otherwise it would not be idle io :-)
    > CFQ doesn't assign request deadlines. That would
    > be another way of handling starvation.

    Keeping IO niceness as similar to CPU niceness as
    you can would be very good for admins.

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