linux-kernel - Re: [PATCH 1/3] x86: increase precision of x86_platform.get/set

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Date:	Tue, 28 May 2013 17:18:01 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	David Vrabel <david.vrabel@...rix.com>
CC:	xen-devel@...ts.xen.org,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] x86: increase precision of x86_platform.get/set_wallclock()

On 05/13/2013 10:56 AM, David Vrabel wrote:
> From: David Vrabel <david.vrabel@...rix.com>
>
> All the virtualized platforms (KVM, lguest and Xen) have persistent
> wallclocks that have more than one second of precision.
>
> read_persistent_wallclock() and update_persistent_wallclock() allow
> for nanosecond precision but their implementation on x86 with
> x86_platform.get/set_wallclock() only allows for one second precision.
> This means guests may see a wallclock time that is off by up to 1
> second.
>
> Make set_wallclock() and get_wallclock() take a struct timespec
> parameter (which allows for nanosecond precision) so KVM and Xen
> guests may start with a more accurate wallclock time and a Xen dom0
> can maintain a more accurate wallclock for guests.
>
> Signed-off-by: David Vrabel <david.vrabel@...rix.com>
> ---
>   arch/x86/include/asm/mc146818rtc.h |    4 ++--
>   arch/x86/include/asm/x86_init.h    |    6 ++++--
>   arch/x86/kernel/kvmclock.c         |    9 +++------
>   arch/x86/kernel/rtc.c              |   17 +++++++----------
>   arch/x86/lguest/boot.c             |    4 ++--
>   arch/x86/platform/efi/efi.c        |   10 ++++++----
>   arch/x86/xen/time.c                |   19 ++++++-------------
>   include/linux/efi.h                |    4 ++--

Just FYI, David: You missed the vrtc code with this conversion.

I finally got around to pushing my current queue to my public tree and 
the kbuild robot noticed the build failure (required INTEL_MID config to 
trigger).

The fix I've queued is here:
https://git.linaro.org/gitweb?p=people/jstultz/linux.git;a=commitdiff;h=52d8e9cc6718ae9e6c44b7723028e4717ba91c8b;hp=1dd5234774b33a17743ae62e8b46b5cd0059e1c7

Let me know if you have any objection or comments on this.

thanks
-john

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