linux-kernel - Re: Regression: can't apply frequency offsets above 1000ppm.

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Date:	Thu, 3 Sep 2015 11:10:20 +0100
From:	Nuno Gonçalves <nunojpg@...il.com>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Miroslav Lichvar <mlichvar@...hat.com>,
	Günter Köllner <dl4mea@...oo.de>,
	stable <stable@...r.kernel.org>
Subject: Re: Regression: can't apply frequency offsets above 1000ppm.

Sorry,

The default chrony config from the debian package can't bring the
clock in sync because it doesn't do steps, and it starts 15 years in
the past. You had some other external help.

Assuming "all factory config" just make sure to disable timesyncd:

sudo systemctl disable systemd-timesyncd

And then reboot in a clean chrony state:

sudo systemctl stop chrony && sudo rm /var/lib/chrony/chrony.drift &&
sudo reboot

You can also just cycle power to get back to year 2000, since the
beaglebone doesn't have a battery backed RTC.

After boot you can see this frequency estimates are allways very large
(usually from +-10.000...80.000):

debian@...1:~$ chronyc sourcestats
210 Number of sources = 4
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
==============================================================================
ftp.claranet.pt             5   3     8 -40146.551     130300  -2720ms    61ms
a88-157-128-22.cpe.netcab   5   3     8 -35628.008     129339  -2393ms    68ms
a212-113-190-2.cpe.netcab   5   3     8 -45213.773     169140  -3057ms    63ms
mirrors.dominios.pt         5   3     8 -39615.191  99995.367  -2694ms    53ms

To have it perform normally try for example 3.16.3:

sudo apt-get install linux-image-3.16.3-bone6

Thanks,
Nuno

On Thu, Sep 3, 2015 at 12:16 AM, John Stultz <john.stultz@...aro.org> wrote:
> On Tue, Sep 1, 2015 at 6:14 PM, Nuno Gonçalves <nunojpg@...il.com> wrote:
>> On Wed, Sep 2, 2015 at 2:03 AM, John Stultz <john.stultz@...aro.org> wrote:
>>> On Tue, Sep 1, 2015 at 5:36 PM, Nuno Gonçalves <nunojpg@...il.com> wrote:
>>>> On Tue, Sep 1, 2015 at 9:25 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>>>>> On Tue, 1 Sep 2015, Nuno Gonçalves wrote:
>>>>>
>>>>>> There is a regression on the clock system since v3.16-rc5-111-g4396e05
>>>>>> [1],
>>>>>
>>>>>> [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4396e058c52e167729729cf64ea3dfa229637086
>>>>>
>>>>> That commit has absolutely nothing to do with NTP. I fear your bisect
>>>>> went down the wrong road somewhere.
>>>>
>>>> You are right. It is v3.16-rc5-114-gdc49159:
>>>>
>>>> http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=dc491596f6394382fbc74ad331156207d619fa0a
>>>>
>>>> I've triple checked it this time. Not sure where I did the mistake to
>>>> get it wrong by 3 commits.
>>>
>>> This commit is much more believable (though surprising as that change
>>> was found to greatly improve results for most uses).
>>>
>>> Can you provide any more details about how the problem is reproduced
>>> (kernel config, what userland images are you using, etc)?  I've got a
>>> BBB myself so I can try to see whats going on.
>>>
>>> thanks
>>> -john
>>
>> I'm using a clean Debian image:
>>
>> https://rcn-ee.com/rootfs/bb.org/testing/2015-08-31/console/bone-debian-8.1-console-armhf-2015-08-31-2gb.img.xz
>>
>> And just installing chrony from the feeds. With any kernel from 3.17
>> you'll have wrong estimates at chronyc sourcestats.
>
> Wrong estimates? Could you be more specific about what the failure
> you're seeing is here? The
>
> I installed the image above, which comes with a 4.1.6 kernel, and
> chrony seems to have gotten my BBB into ~1ms sync w/ servers over the
> internet fairly quickly (at least according to chronyc tracking).
>
> root@...glebone:~# chronyc tracking
> Reference ID    : 198.110.48.12 (time01.muskegonisd.org)
> Stratum         : 3
> Ref time (UTC)  : Wed Sep  2 23:07:05 2015
> System time     : 0.001320852 seconds fast of NTP time
> Last offset     : +0.001209910 seconds
> RMS offset      : 0.002978454 seconds
> Frequency       : 44.684 ppm fast
> Residual freq   : +0.068 ppm
> Skew            : 1.223 ppm
> Root delay      : 0.073661 seconds
> Root dispersion : 0.021902 seconds
> Update interval : 518.3 seconds
> Leap status     : Normal
> root@...glebone:~# chronyc sourcestats
> 210 Number of sources = 4
> Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
> ==============================================================================
> 172.82.134.51               4   3   17m     +1.593     30.515   +798us   802us
> unlawful.id.au              6   5   21m     +1.080      2.312  +2731us   273us
> time.theplante.net         11   5   77m     -0.536      0.915  -1165us  1044us
> time01.muskegonisd.org      4   3   25m     +1.677     15.256   -342us   516us
>
>
> Can you send me your kernel config?
>
> thanks
> -john
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