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

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Date:	Thu, 11 Nov 2010 22:51:23 +0200
From:	Alexander Shishkin <virtuoso@...nd.org>
To:	Valdis.Kletnieks@...edu
Cc:	linux-kernel@...r.kernel.org, John Stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kay Sievers <kay.sievers@...y.org>, Greg KH <gregkh@...e.de>,
	Chris Friesen <chris.friesen@...band.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Shishkin <virtuoso@...nd.org>
Subject: Re: [PATCHv6 0/7] system time changes notification

On Thu, Nov 11, 2010 at 03:28:13PM -0500, Valdis.Kletnieks@...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.

Regards,
--
Alex
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