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Feature #9439

Poll Interval For GPS and PPS

Added by Pierre Poutine about 1 year ago. Updated about 2 months ago.

Status:
New
Priority:
Normal
Assignee:
-
Category:
NTPD
Target version:
-
Start date:
03/28/2019
Due date:
% Done:

0%

Estimated time:

Description

The default minpoll and maxpoll for GPS and PPS in /etc/inc/system.inc is set to 4. These should both be set to 3. This will reduce the interval from 16s to 8s.

History

#1 Updated by Jim Pingle 9 months ago

  • Assignee set to Jim Pingle

#2 Updated by Jim Pingle 9 months ago

The documentation for ntpd says the minimum value is 4. Have you tried 3?

Though this value should probably be adjustable at least, I can add fields with the current values to the main settings and GPS/PPS tabs.

If we determine the lower values do work then it's just a matter of adjusting the defaults once that's done.

#3 Updated by Jim Pingle 9 months ago

  • Status changed from New to Feedback

The GUI part of this is I mentioned is in #6787

This can remain open to investigate whether or not values less than 4 are possible/viable.

#4 Updated by Pierre Poutine about 2 months ago

Jim Pingle wrote:

The GUI part of this is I mentioned is in #6787

This can remain open to investigate whether or not values less than 4 are possible/viable.

3 works great. You need a GPS/PPS! I just upgraded to 2.5.0 and saw the new menu which is nice.
You left the defaults at 4 which is fine but you didn't have a menu option for 3.
$ntp_poll_min_value = 4 can be changed to 3 in system.inc. Then 4 is still the default for gps/pps but 3 will be an option in the menus.

#5 Updated by Jim Pingle about 2 months ago

  • Status changed from Feedback to New
  • Assignee deleted (Jim Pingle)
  • Target version deleted (2.5.0)

What advantage would 3 have over 4 when using a local GPS though? Why would it need to probe that frequently?

If we do add an option for 3, it would need input validation to require that it only be set when using a local GPS then. Otherwise it seems like people might be too tempted to set it low when polling remote servers which would put an undue burden on public NTP servers.

#6 Updated by Pierre Poutine about 2 months ago

Jim Pingle wrote:

What advantage would 3 have over 4 when using a local GPS though? Why would it need to probe that frequently?

If we do add an option for 3, it would need input validation to require that it only be set when using a local GPS then. Otherwise it seems like people might be too tempted to set it low when polling remote servers which would put an undue burden on public NTP servers.

3 offers reduced jitter over 4. It is the capability of ntpd and shouldn't be omitted. Low poll interval is also valuable for polling a server on a low latency network like a LAN. The current menus offer 4 already which is lower than the defaults and not recommended for public pool servers. I run a stratum 1 server in the public NTP pool and personally have no problem with users legitimately polling every 8 seconds especially if they are low latency.

#7 Updated by Jim Pingle about 2 months ago

3 offers reduced jitter over 4.
Low poll interval is also valuable for polling a server on a low latency network like a LAN.

OK

It is the capability of ntpd and shouldn't be omitted.

That may be but it's not the documented capability. Their docs say minimum is 4. My concern is that we'd be going against their own advice. But it's also possible that their docs are wrong/outdated.

The current menus offer 4 already which is lower than the defaults and not recommended for public pool servers.

Yes but 4 is not the default and 4 is what their documentation says should be the minimum.

I run a stratum 1 server in the public NTP pool and personally have no problem with users legitimately polling every 8 seconds especially if they are low latency.

That may be true for you, but you cannot speak for every public server operator.

#8 Updated by Pierre Poutine about 2 months ago

Here is a link to the official documentation: https://www.eecis.udel.edu/~mills/ntp/html/poll.html
The FreeBSD documentation is out of date.

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