Re: [chrony-dev] [GIT] chrony/chrony.git branch, master, updated. 2.4-9-g6cd5583

[Bill Unruh <unruh@xxxxxxxxxxxxxx>]

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/

On Thu, 30 Jun 2016, Miroslav Lichvar wrote:

> On Thu, Jun 30, 2016 at 08:32:16AM -0700, Bill Unruh wrote:
> > One really weird effect I found was that I have one machine connected to a
> > Sure GPS, which seems to have quite a large fluctuation. (or for which the
> > interrupt processing seems to have a large fluctuation-- impossible to figure
> > out which of course.) but a few times this week, for hours at a time ( 3-6
> > hrs) the GPS time seems to be much smoother (the fluctuations in slope are
> > much less) and at the same time, the delay times to the other machines are
> > smaller, and no longer bimodal. (the delay time seems to have two clumps
> > aroung 16us and 24us-- see for example boson in the graphs-- the lower graph
> > is the offset(blue)  and the delay(pink) Note that the transition to bimodal
> > is at the same time as the GPS slope becomes much noisier (info is the gps
> > driven one-- using the serial port interrupt with the Linux serial port driver. )
> > The only thing I could imagine is that there is something messing with the
> > interupts which affects both the serial port interrupts and the network card
> > interrups at the same time.  Anyone seen anything like this befoe?
>
> Was there a CPU intensive task running on the server in those
> intervals? CPU needs more time to wake up from deep power-saving
> states, so this might have an effect on accuracy of timestamping of
> both NIC and PPS interrupts. On some machines, I can see offset of NTP
> sources jump by few tens of microseconds when I start a program that
> fully loads the CPU.

Nope, not that I know of. The times were at night (the times are in UTC) but
extend into the day-- eg the first quiet time is from about 10AM UTC to 11PM
UTc(which is 7 hours ahead of my time) on Jun 28 then from 6AM to 6PM on the
29. Ie it is not periodic and there was nothing untoward going on at that
time. 
And you canclearly see the bimodal pattern on the scatter plots at the bottom
of the page. 
Oh, I realise I did not give the page
www.theory.physics.ubc.ca/chrony/chrony.html


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