linux-kernel - Re: [PATCH 5/5] x86/xen: sync the CMOS RTC as well as the Xen wallclock

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Date:	Fri, 28 Jun 2013 17:51:17 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	<xen-devel@...ts.xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	<linux-kernel@...r.kernel.org>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: [PATCH 5/5] x86/xen: sync the CMOS RTC as well as the Xen wallclock

On 28/06/13 17:09, Thomas Gleixner wrote:
> On Fri, 28 Jun 2013, David Vrabel wrote:
>>
>> Before:
>>
>> Xen wallclock set when time is stepped.
>> Xen wallclock set every 11 minutes (by sync_cmos_clock()).
>> Hardware RTC never set.
>>
>> After:
>>
>> Xen wallclock set when time is stepped.
>> Xen wallclock set every 11 minutes (in pvclock gtod notifier).
> 
> Ah, you are emulating the sync_cmos_clock() behaviour for the xen
> wallclock via the periodic pvclock_gtod notifier call.
> 
>> Hardware RTC set every 11 minutes (by sync_cmos_clock()).
>>
>> I'll update the changelog to be more descriptive:
>>
>>   Adjustments to Xen's persistent clock via update_persistent_clock()
>>   don't actually persist, as the Xen wallclock is a software only clock
>>   and modifications to it do not modify the underlying CMOS RTC.
>>
>>   The x86_platform.set_wallclock hook can be used to keep the hardware
>>   RTC synchronized (as on bare metal).  If (in dom0) we make the Xen
>>   wallclock periodically synchronized by the pvclock_gtod notifier, the
>>   set_wallclock hook need not update the Xen wallclock and the native
>>   implementation can be used.
> 
> Yep. I'll pick that up.

If it helps, I've made this change as well as splitting the xen part of
the hrtimers patch out into a separate commit.

The following changes since commit 52efa9eb9ea36b457b23b1b5d3dd9ce64d110715:

  x86: increase precision of x86_platform.get/set_wallclock() (2013-06-26 18:07:16 +0100)

are available in the git repository at:
  git://xenbits.xen.org/people/dvrabel/linux.git wallclock-v8

David Vrabel (6):
      hrtimers: support resuming with two or more CPUs online (but stopped)
      time: pass flags instead of multiple bools to timekeeping_update()
      time: indicate that the clock was set in the pvclock gtod notifier chain
      xen: remove unnecessary call to clock_was_set() during resume
      x86/xen: sync the wallclock when the system time is set
      x86/xen: sync the CMOS RTC as well as the Xen wallclock

 arch/x86/xen/time.c          |   42 +++++++++++++++++++++++++++++++++++-------
 drivers/xen/manage.c         |    3 ---
 include/linux/pvclock_gtod.h |    7 +++++++
 kernel/hrtimer.c             |   15 ++++++++++++---
 kernel/time/timekeeping.c    |   39 ++++++++++++++++++++++++---------------
 5 files changed, 78 insertions(+), 28 deletions(-)

David
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