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

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Date:	Wed, 2 Sep 2015 16:16:00 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Nuno Gonçalves <nunojpg@...il.com>
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.

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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