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

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Message-ID: <20130528202527.GB23266@phenom.dumpdata.com>
Date:	Tue, 28 May 2013 16:25:27 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	David Vrabel <david.vrabel@...rix.com>,
	Jan Beulich <JBeulich@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"xen-devel@...ts.xen.org" <xen-devel@...ts.xen.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 2/3] timekeeping: sync persistent clock and
 RTC on system time step changes

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@...hat.com>
Date:   Thu Feb 14 12:02:54 2013 -0500

    x86: Do full rtc synchronization with ntp

which is not CC-ed to stable@...r.kernel.org, so the #1 patch would
not be able to be back-ported to any kernel right (so v3.9, v3.8..)?

But it could go to v3.10 - as that change is there. But you are saying
it can't go to v3.10 b/c the interface change is not a bugfix
material.  Is that b/c said git commit might cause regressions and
you wouldn't want to do two reverts?

That makes sense -  which point I  you are right that it makes
sense to stick said patch (#1) in your 3.11 queue and skip the v3.10
train for it.
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