Re: [Xen-devel] [PATCH 2/3] timekeeping: sync persistent clock and RTC on system time step changes

[John Stultz <john.stultz@xxxxxxxxxx>]

On 05/28/2013 01:25 PM, Konrad Rzeszutek Wilk wrote:
> On Tue, May 28, 2013 at 01:11:33PM -0700, John Stultz wrote:
> > On 05/28/2013 01:03 PM, John Stultz wrote:
> > > On 05/28/2013 12:48 PM, Konrad Rzeszutek Wilk wrote:
> > > > On Tue, May 28, 2013 at 12:09:14PM -0700, John Stultz wrote:
> > > > > On 05/28/2013 11:31 AM, Konrad Rzeszutek Wilk wrote:
> > > > > > On Tue, May 28, 2013 at 07:26:14PM +0100, David Vrabel wrote:
> > > > > > > On 15/05/13 19:10, John Stultz wrote:
> > > > > > > > Ok, so really, as soon as the Dom0 time is set by NTP,
> > > > > > > > all guests will
> > > > > > > > see the right time? That makes more sense, and means the window for
> > > > > > > > these sorts of issues is reasonably quite small.
> > > > > > > It's a small window but it's occurring in our automated test system.
> > > > > > >
> > > > > > > > David: So I'm less inclined to merge this individual
> > > > > > > > change, but if you
> > > > > > > > still feel strongly about it, let me know and we can
> > > > > > > > circle around on it
> > > > > > > > after you've addressed the specific issues I pointed out earlier.
> > > > > > > This patch was the actual bug fix but I've reworked it to use the
> > > > > > > pvclock_gtod notifier chain as this seemed to be what KVM hosts were
> > > > > > > using to maintain a clock for guests.  Please review the
> > > > > > > new series, thanks.
> > > > > > Looks good.
> > > > > >
> > > > > > John if you are OK I am thinking to push this to Linus
> > > > > > shortly as it is
> > > > > > fixing a bug.
> > > > > I'm really not sure I'd call this a bug.  That seems like an
> > > > > over-reaction to a misconfigured system.
> > > > >
> > > > > Or if there is a bug, I'm not sure its been clearly explained.
> > > > The #1 patch - b/c you try to set the RTC time and it actually
> > > > never takes. Meaning
> > > > on the next time the machine is booted the time is again off.
> > > Ok. Yea, that one I'm fine with and have queued for 3.11.
> > >
> > > If you want to push it as a bug fix for 3.10, I'll leave it to you
> > > to push to Linus.
> > Probably obvious, but just in case its not clear:
> >
> > Though if that one patch goes to linus for 3.10, it needs to be
> > reworked to not depend on the mach_set_rtc_mmss() interface change
> > it currently depends on. The interface change is not bugfix
> > material.
> You are referring to commit 3195ef59cb42cda3aeeb24a7fd2ba1b900c4a3cc
> Author: Prarit Bhargava <prarit@xxxxxxxxxx>
> Date:   Thu Feb 14 12:02:54 2013 -0500
>
>      x86: Do full rtc synchronization with ntp
No. I mean David's patch:
    x86: Increase precision of x86_platform.get/set_wallclock()

That one should be held back for 3.11.

But the calling of mach_set_rtc_mmss() from the Xen set_wallclock hook 
would still be reasonable to go in 3.10 (limited impact to only Xen, 
fixing a bug), but it would have to limit the call to the second 
granular mach_set_rtc_mmss() in 3.10.
thanks
-john

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