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    SubjectRe: [RFC 2/5] sched: Add CPU rate soft caps
    Peter Williams wrote:
    > Balbir Singh wrote:
    >> On 5/26/06, Peter Williams <pwil3058@bigpond.net.au> wrote:
    >> <snip>
    >>>
    >>> Notes:
    >>>
    >>> 1. To minimize the overhead incurred when testing to skip caps
    >>> processing for
    >>> uncapped tasks a new flag PF_HAS_CAP has been added to flags.
    >>>
    >>> 2. The implementation involves the addition of two priority slots to the
    >>> run queue priority arrays and this means that MAX_PRIO no longer
    >>> represents the scheduling priority of the idle process and can't be
    >>> used to
    >>> test whether priority values are in the valid range. To alleviate this
    >>> problem a new function sched_idle_prio() has been provided.
    >>
    >> I am a little confused by this. Why link the bandwidth expired tasks a
    >> cpu (its caps) to a priority slot? Is this a hack to conitnue using
    >> the prio_array? why not move such tasks to the expired array?
    >
    > Because it won't work as after the array switch they may get to run
    > before tasks who aren't exceeding their cap (or don't have a cap).

    Another important reason for using these slots is that it allows waking
    tasks to preempt tasks that have exceeded their cap.

    Peter
    --
    Peter Williams pwil3058@bigpond.net.au

    "Learning, n. The kind of ignorance distinguishing the studious."
    -- Ambrose Bierce
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