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    SubjectRe: [REPORT] cfs-v4 vs sd-0.44

    * Ingo Molnar <> wrote:

    > (we obviously dont want to allow people to 'share' their loans with
    > others ;), nor do we want to allow a net negative balance. CFS is
    > really brutally cold-hearted, it has a strict 'no loans' policy - the
    > easiest economic way to manage 'inflation', besides the basic act of
    > not printing new money, ever.)

    sorry, i was a bit imprecise here. There is a case where CFS can give
    out a 'loan' to tasks. The scheduler tick has a low resolution, so it is
    fundamentally inevitable [*] that tasks will run a bit more than they
    should, and at a heavy context-switching rates these errors can add up
    significantly. Furthermore, we want to batch up workloads.

    So CFS has a "no loans larger than sched_granularity_ns" policy (which
    defaults to 5msec), and it captures these sub-granularity 'loans' with
    nanosec accounting. This too is a very sane economic policy and is
    anti-infationary :-)


    [*] i fundamentally hate 'fundamentally inevitable' conditions so i
    have plans to make the scheduler tick be fed from the rbtree and
    thus become a true high-resolution timer. This not only increases
    fairness (=='precision of scheduling') more, but it also decreases
    the number of timer interrupts on a running system - extending
    dynticks to sched-ticks too. Thomas and me shaped dynticks to enable
    that in an easy way: the scheduler tick is today already a high-res
    timer (but which is currently still driven via the jiffy mechanism).
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      Last update: 2007-04-23 22:49    [W:0.021 / U:5.744 seconds]
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