[chrony-users] Re: GPS performance tuning of `offset`

[ Thread Index | Date Index | More chrony.tuxfamily.org/chrony-users Archives ]

Hi all,

Just want to know which is the correct approach to set the refclock `offset` parameter.  Out of the values in the table below, should I use the minimum, maximum, average or something else?

Are there any consequences if I use too small or too large a value?  eg. 0.3 v 0.4 or 0.5

Thanks, Brendan.

On 31/3/19 9:17 am, Brendan Simon wrote:
I have enabled a number of NTP servers and set my refclock to no select and long polls, etc.

pool au.pool.ntp.org iburst

refclock SHM 0 refid GPS poll 8 filter 1000 noselect

Here are the results of `chrony sourcestats` taken at random times (between 8-24 hours)

210 Number of sources = 11
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
GPS                        10   6   38m    +15.400     26.236   +340ms    12ms
GPS                        11   6   42m     +7.051     29.254   +325ms    16ms
GPS                        18  10   73m     +9.280      7.530   +396ms  9851us
GPS                        10   6   37m    +28.219     44.829   +407ms    15ms
GPS                        26  14  107m     +1.894      4.626   +394ms    13ms
GPS                        26  12  107m     -2.719     11.015   +373ms    26ms

The offset ranges between 325ms to 407ms.  Is it best to use the minimum, median or maximum value.  Or does it not matter much?

In my mind I think it might be better to use the minimum value, so that an offset adjustment doesn't cause the calculated time to go back to previous second.  That may be a false/wrong assumption of how things work.

Thanks, Brendan.

Mail converted by MHonArc 2.6.19+ http://listengine.tuxfamily.org/