Re: [PATCHv6 0/7] system time changes notification

[Thomas Gleixner <tglx@linutronix.de>]

B1;2401;0cOn Thu, 11 Nov 2010, Alexander Shishkin wrote:

> On Thu, Nov 11, 2010 at 03:28:13PM -0500, Valdis.Kletnieks@vt.edu wrote:
> > On Thu, 11 Nov 2010 21:29:55 +0200, Alexander Shishkin said:
> > 
> > > Consider we want stuff like "wakeup every day at 3pm", the next wakeup
> > > might be earlier than the timer we calculated last time, on system
> > > time changes. We need to re-calculate it. This is necessary for all
> > > repeating events.
> > > 
> > > Say we want to wakeup at 3pm, now it's 4pm, so we schedule it in 23
> > > hours. Now the system time changes to 2pm, and we would expect to
> > > wakeup in one hour, but we take 25.
> > 
> > Sorry, I tuned in late here...
> > 
> > So the plan is that if you're not using this new interface, it will go off at
> > the same absolute offset (23 hours after timer was set), but if you're using
> > this interface, your timer event gets interrupted, you get woken up (say)
> > 15 hours into your 23, and it's your job to decide if you need to set a
> > new timer for the remaining 6, 7, 8 hours or some other number?
> 
> Yes. This interface doesn't deal with timers, it only provides notifications.

The notification itself is pointless unless your application is
dealing with timers which need to be adjusted the one way or the
other.

That said, I'm still not convinced that this usecase justifies a new
systemcall.

1) We can make timers wake up when a clock change happens
2) Can't we use existing notification stuff like uevents or such ?

Thanks,

	tglx