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    SubjectRe: [patch 6/13] signal/timer/event fds v9 - timerfd core ...
    On Mon, 2007-04-02 at 10:30 -0700, Davide Libenzi wrote:

    > > There is no inaccuracy when you rearm the timer on read: hrtimer_forward
    > > takes care, that the period is accurate. It does not start the timer out
    > > of the periodic order, i.e. on a different time frame.
    > >
    > > Where is the win of keeping the timer running, when nobody cares about
    > > the expiry at all ? It just generates interrupts and events for nothing.
    > Then you'd lose the ability to know if you lost one or more (yes, you
    > could figure it out by reading the time and with a few calculations). I
    > think that the capping (to a sane value) idea solves the DoS issue and at
    > the same time have the ability to report you missed ticks. What are your
    > strong points against that solution?

    Err, the read function

    ticks = hrtimer_forward(&ctx->tmr, ktime_get(),

    does give you the number of (lost) ticks.

    tmr->expires holds the absolute expiry time of the last event.
    hrtimer_forward() adds N intervals to tmr->expires, so that the new
    tmr->expires value is greater than now (ktime_get()). It returns N.

    So the number of lost ticks is N - 1. No time reading and no magic
    math :)


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