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    SubjectRe: HZ question


    On Tue, 13 Sep 2005, Mark Hounschell wrote:

    > On a 100HZ kernel ANY requested delay via udelay or
    > pthread_cond_timedwait of less than 10000usecs is unreliable and the the
    > actual results are totally unacceptable.
    >
    > On a 1000HZ kernel the number is 1000 usecs.
    >
    > I'm not asking the kernel running at 1000hz to actually give me 500 usec
    > delay if I ask. I do expect it to be at least 500 usec and within +- a
    > single HZ however.

    The kernel just cannot guarantee the latter. Rounding is only one of
    many issues here.
    Do you also want to know about CONFIG_PREEMPT, SMP, current load, future
    load in order to estimate the delay you want to ask for?

    OTOH, I'm not a soft real-time expert, so I'll stop commenting here.

    Tim
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