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

From: Thomas Gleixner <tglx@linutronix.de>
To: David Vrabel <david.vrabel@citrix.com>
Cc: xen-devel@lists.xen.org,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	linux-kernel@vger.kernel.org,
	John Stultz <john.stultz@linaro.org>
Subject: Re: [PATCH 5/5] x86/xen: sync the CMOS RTC as well as the Xen wallclock
Date: Fri, 28 Jun 2013 18:09:15 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.02.1306281805430.4013@ionos.tec.linutronix.de> (raw)
In-Reply-To: <51CDB0A1.6080409@citrix.com>

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