Re: [chrony-dev] [GIT] chrony/chrony.git branch, master, updated. 1.26-26-g9a01ccc

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

I am a bit confused both about the reason for and the details of this
alteration. chrony determines both the offset error and the frequency error.
It corrects the frequency error immediately, and then adjusts the frequency to
eliminate the offset error. I am not sure what the reason is behind the
"eliminate small errors over a long time, and large errors quickly". This
looks like it is heading for the step type adjustment of ntpd for larger
offset errors. Is your thinking that small errors are probably not true
offsets but noise and thus should not really be corrected? What are the
consequences of this change to the stability of the system?



On Tue, 15 Nov 2011, git@xxxxxxxxxxxxx wrote:

> This is an automated email from git. It was enerated because a ref
> change was pushed to the repository "chrony/chrony.git".
>
> The branch, master has been updated
>       via  9a01ccc07fd5399be88218c02a0430d30cefd82b (commit)
>       via  1b8deaf3547c86efd3ac567aba8fc0a5a28d79be (commit)
>       via  c7d0232bb113c6ca86cd24f9e694c70bfc946ab2 (commit)
>       via  79e5f2be1331fb639362cd159087343c06594351 (commit)
>      from  9ab181eb9c75e42695f60c1f89bc2a6235bcfc96 (commit)
>
> Those revisions listed above that are new to this repository have
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> - Log -----------------------------------------------------------------
> commit 9a01ccc07fd5399be88218c02a0430d30cefd82b
> Author: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
> Date:   Tue Nov 15 12:24:50 2011 +0100
>
>    Add corrtimeratio directive
>
>    The corrtimeratio directive controls the ratio between the
>    duration in which the clock is slewed for an average correction
>    according to the source history and the interval in which the
>    corrections are done (usually the NTP polling interval).  Corrections
>    larger than the average take less time and smaller corrections take
>    more time, the amount of the correction and the correction time are
>    inversely proportional.
>
>    Increasing corrtimeratio makes the overall frequency error of
>    the system clock smaller, but increases the overall time error as
>    the corrections will take longer.
>
>    By default, the ratio is 1, which means the duration of an average
>    correction will be close to the update interval.
>
> commit 1b8deaf3547c86efd3ac567aba8fc0a5a28d79be
> Author: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
> Date:   Tue Sep 13 14:53:46 2011 +0200
>
>    Control offset correction rate in Linux driver
>
>    The kernel currently doesn't support a linear adjustment with
>    programmable rate, extend the use of the kernel PLL with locked
>    frequency instead.
>
>    Set the PLL time constant according to the correction time corresponding
>    to the correction rate and corrected offset.
>
>    On kernels with nano PLL adjtime() is no longer used.
>
> commit c7d0232bb113c6ca86cd24f9e694c70bfc946ab2
> Author: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
> Date:   Mon Sep 5 15:45:32 2011 +0200
>
>    Introduce offset correction rate
>
>    We want to correct the offset quickly, but we also want to keep the
>    frequency error caused by the correction itself low.
>
>    Define correction rate as the area of the region bounded by the graph of
>    offset corrected in time. Set the rate so that the time needed to correct
>    an offset equal to the current sourcestats stddev will be equal to the
>    update interval (assuming linear adjustment). The offset and the
>    time needed to make the correction are inversely proportional.
>
>    This is only a suggestion and it's up to the system driver how the
>    adjustment will be executed.
>
> commit 79e5f2be1331fb639362cd159087343c06594351
> Author: Miroslav Lichvar <mlichvar@xxxxxxxxxx>
> Date:   Fri Nov 11 18:40:01 2011 +0100
>
>    Include clock steps in calculated reference update interval
>
> -----------------------------------------------------------------------
>
> Summary of changes:
> acquire.c       |    2 +-
> chrony.texi     |   30 +++++++++++++++++++++
> cmdmon.c        |    2 +-
> conf.c          |   21 +++++++++++++++
> conf.h          |    1 +
> local.c         |   10 +++---
> local.h         |    7 +++--
> localp.h        |    5 ++-
> reference.c     |   64 +++++++++++++++++++++++++++++++++++++++-------
> reference.h     |    1 +
> rtc_linux.c     |    2 +-
> sources.c       |    1 +
> sys_linux.c     |   76 +++++++++++++++++++++++++++++++++++++++++++++++--------
> sys_netbsd.c    |    2 +-
> sys_solaris.c   |    2 +-
> sys_sunos.c     |    2 +-
> wrap_adjtimex.c |    4 +-
> wrap_adjtimex.h |    2 +-
> 18 files changed, 194 insertions(+), 40 deletions(-)
>
>
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--
William G. Unruh   |  Canadian Institute for|     Tel: +1(604)822-3273
Physics&Astronomy  |     Advanced Research  |     Fax: +1(604)822-5324
UBC, Vancouver,BC  |   Program in Cosmology |     unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1     |      and Gravity       |  www.theory.physics.ubc.ca/

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