linux-kernel - Re: [tip:timers/core] timerfd: Allow timers to be cancelled when clock was set

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Date:	Wed, 11 May 2011 16:48:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kay Sievers <kay.sievers@...y.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...hat.com, hpa@...or.com,
	johnstul@...ibm.com, davidel@...ilserver.org, virtuoso@...nd.org,
	tglx@...utronix.de, chris.friesen@...band.com,
	kirill@...temov.name, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:timers/core] timerfd: Allow timers to be cancelled when
 clock was set

On Wed, 2011-05-11 at 16:32 +0200, Kay Sievers wrote:
> On Wed, May 11, 2011 at 16:30, Peter Zijlstra <peterz@...radead.org> wrote:
> > On Wed, 2011-05-11 at 16:22 +0200, Kay Sievers wrote:
> >> On Wed, May 11, 2011 at 16:01, Peter Zijlstra <peterz@...radead.org> wrote:
> >> > On Wed, 2011-05-11 at 15:52 +0200, Kay Sievers wrote:
> >> >>
> >> >> No, fixed time spans have never been a problem, and are not the
> >> >> example here. It's about the normal wall clock, that wakes up every
> >> >> minute and updates the numbers on the screen.
> >> >
> >> > 'wakes up every minute' sounds like a fixed time interval to me.
> >>
> >> Right, but if the wall clock changes, it must not wait for the full
> >> minute to update the numbers, they need to update immediately with the
> >> new wall clock time. Stuff woke up every second in the past to do
> >> that, but that's not what we want today.
> >
> > Again, nothing that couldn't be solved with a notifier of sorts.
> 
> Right. What we have with that patch, and what's visible to the
> outside, is nothing but such a notifier. What kind of interface you
> have in mind instead?

Dunno, an eventfd that triggers every time someone calls adjtime() and
related?

Anything as long as it doesn't increase HRTIMER_MAX_CLOCK_BASES really.

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