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

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Date:	Thu, 11 Nov 2010 15:28:13 -0500
From:	Valdis.Kletnieks@...edu
To:	Alexander Shishkin <virtuoso@...nd.org>
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>
Subject: Re: [PATCHv6 0/7] system time changes notification

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?

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