linux-kernel - Re: [PATCH 2/4] time: add a notifier chain for when the system time is stepped

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Message-ID: <20130619171321.GE13046@phenom.dumpdata.com>
Date:	Wed, 19 Jun 2013 13:13:21 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	David Vrabel <david.vrabel@...rix.com>, xen-devel@...ts.xen.org,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/4] time: add a notifier chain for when the system time
 is stepped

On Wed, Jun 19, 2013 at 09:52:06AM -0700, John Stultz wrote:
> On 06/19/2013 08:25 AM, David Vrabel wrote:
> >From: David Vrabel <david.vrabel@...rix.com>
> >
> >The high resolution timer code gets notified of step changes to the
> >system time with clock_was_set() or clock_was_set_delayed() calls.  If
> >other parts of the kernel require similar notification there is no
> >clear place to hook into.
> >
> >Add a clock_was_set atomic notifier chain
> >(clock_was_set_notifier_list) and call this in place of
> >clock_was_set().  If the timekeeping locks are held, the calls are
> >deferred to a new tasklet.
> >
> >The hrtimer code adds a notifier block to this chain and uses it to
> >call (the now internal) clock_was_set().  Since the timekeeping code
> >does not call the chain from the timer irq clock_was_set_delayed() and
> >associated code can be removed.
> 
> So on my initial quick review, this *looks* pretty reasonable. I get
> a little worried about interface abuse (ie: random drivers trying to
> hook into clock_was_set_notifier_list), but we can move that into
> timekeeper_internal.h or something similar to limit that.
> 
> The other issue here is we've been burned pretty badly in the past
> with changes to clock_was_set(), as its key to keeping timers in
> line with timekeeping.  So this will need a fair amount of testing
> and run time before this gets merged, so 3.12 is what we'd be
> targeting at the earliest (its getting a bit late for taking changes
> for 3.11 anyway).

I think we have four weeks left? Or you think Linus is going to release
at the end of the month?
> 
> If you want to try to push patch 1/4 in for 3.11 via the Xen tree,

Done.
> I'll see about queuing the other three for hopefully 3.12.

OK, let me run them through the testing gauntleet to have the
warm fuzzy feeling.
> 
> thanks
> -john
> 
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