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

[John Stultz <john.stultz@xxxxxxxxxx>]

On 06/19/2013 10:13 AM, Konrad Rzeszutek Wilk wrote:
> 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@xxxxxxxxxx>
> > >
> > > 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?
Well, I have to queue it, and then get Thomas to pull it from me, and 
that can take some time. And after -rc6 there's just not a lot of time 
for things to get testing in -next before being pushed to Linus. Its 
just a bit rushed for me.

> > 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.  I'll be running it through my test cases as well.

-john

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