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 18:09:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	David Vrabel <david.vrabel@...rix.com>
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 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.

Thanks,

	tglx
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