| Re: [chrony-dev] [GIT] chrony/chrony.git branch, master, updated. 1.26-26-g9a01ccc |
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On Tue, 15 Nov 2011, Miroslav Lichvar wrote:
On Tue, Nov 15, 2011 at 06:55:18PM +0100, git@xxxxxxxxxxxxx wrote:
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.
I'm not sure about the terminology and I'm open for suggestions for a
better name for this option.
In my testing the RMS frequency error can improve by factor 10 or even
more and with larger corrtimeratio it can be even better than with ntpd.
It seems there is always a compromise between time and frequency
error. The default is set so the time error is not noticeably worse
than it was before.
The graphs of the clock offset now look much nicer too:
http://mlichvar.fedorapeople.org/tmp/chrony_corr.png
Why the large jump in time offset at the beginning with the new procedure.
That looks suspicious. Also the oscillations in the time, while damped do not
look very strongly damped. (Q of maybe 10)
--
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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