linux-kernel - Re: [PATCH] time, Fix setting of hardware clock in NTP code

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Message-ID: <51158F5E.9000007@linaro.org>
Date:	Fri, 08 Feb 2013 15:50:54 -0800
From:	John Stultz <john.stultz@...aro.org>
To:	Prarit Bhargava <prarit@...hat.com>
CC:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] time, Fix setting of hardware clock in NTP code

On 02/08/2013 03:44 PM, Prarit Bhargava wrote:
>
> On 02/08/2013 06:12 PM, John Stultz wrote:
>> On 02/08/2013 02:59 PM, Prarit Bhargava wrote:
>> Ok, I've got this queued in my tree. What sort of testing did you do with it?
>>
>> I want to make sure we don't run into any bad interactions with the existing
>> 15min cap on x86.
> John,
>
> I did the following:
>
> I used powerpc pseries systems and tested this using both positive and negative
> values of sys_tz.minuteswest, with both UTC and LOCAL in /etc/adjtime.  I dumped
> values of 'hwclock -D' and date and confirmed that I no longer see time
> increasing by sys_tz.minuteswest each reboot.
>
> I also tested x86 32-bit and 64-bit as a sanity check and verified that the
> current behaviour on those arches is the same; ie) I don't see *any* impact to
> the x86 rtc.  I dumped values of 'hwclock -D' and date, and again confirmed that
> I see no differences in values.  I did that with both UTC and LOCAL.
>
> I also tested a powerpc box and set the hwclock (via BIOS) back to Dec 6 2012 to
> see what would happen when I enabled ntp.  The system booted, set the system
> time to Dec 6 2012, and then properly ended up with both system time AND hwclock
> as Feb 8 2013 after systemd init .... (The *exact* time-of-day was correct as
> well.  I just can't remember the time I did it ;) )
>
> And I did the same thing (adjusting the BIOS date back) on x86. I only see the
> hours and minutes change, as we expect.  The year, month, day are unaffected
> with both UTC and LOCAL.
>
> tl;dr  Yup.  Tested as much as I could think of doing before submitting.  Tested
> on a both x86, powerpc.  Fixed the bug on powerpc.  No change in behavior seen
> with x86.
Great! This is perfect!

Thanks for being so thorough!
-john

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