[ntp:questions] Performance estimation

William Unruh unruh at invalid.ca
Mon Jun 15 18:58:08 UTC 2020

On 2020-06-15, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 15/06/2020 08:33, Miroslav Lichvar wrote:
>> On 2020-06-14, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
>>> When using the ntpq -crv command, which is the better measure of system
>>> performance - clk_jitter or sys_jitter?  I've look for the definitions
>>> and I'm thinking sys_jitter but perhaps someone could please remind me
>>> of the difference?
>> clk_jitter seems to be the jitter of the system clock as it is being
>> updated with offsets, and sys_jitter seems to be the jitter of the
>> selected peer, or the combined peers after clustering.
>> https://www.eecis.udel.edu/~mills/ntp/html/cluster.html
> [Been trying to send through e-mail to ntp-questions, but anything I 
> send gets rejected!]
> Thanks, Miroslav.  Right!  I'm not sure which I should be measuring so I
> plotted both:
>    https://www.satsignal.eu/mrtg/performance_ntp_jitter.php
> Blue is system jitter, green is clock jitter.
> The lightly-loaded Raspberry Pi cards are all showing low numbers of 
> jitter, and it would be really useful to get that in more than three 
> decimal places of milliseconds.

Why would it be useful? What are you trying to do. It is always better
to first present the problem rather than trying to get people to improve
your solution to an unknown problem.


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