Messages in this thread | | | Subject | Re: [patch 6/13] signal/timer/event fds v9 - timerfd core ... | From | Thomas Gleixner <> | Date | Mon, 02 Apr 2007 19:47:44 +0200 |
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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(), ctx->tintv);
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 :)
tglx
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