Re: PSA: Clock drift and pkgin

On 2023-12-21 13:53, Jan-Benedict Glaw wrote:
> On Thu, 2023-12-21 12:49:06 +0100, Johnny Billquist <[email protected]> wrote:
>> On 2023-12-21 12:14, Jan-Benedict Glaw wrote:
>>> On Thu, 2023-12-21 10:44:22 +0000, Maciej W. Rozycki <[email protected]> wrote:
>>>> On Wed, 20 Dec 2023, Maciej W. Rozycki wrote:
>>
>> [...]
>>
>>> Looking at the numbers, I wonder about multiple issues here. Why did
>>> the jitter values rise up that much, while the delay keeps its value?
>>
>> Unless I remember wrong, delay is merely how long it takes for packets to
>> travel back and forth to the ntp server. So it has no relation to jitter or
>> offset. It would rather be weird if delay suddenly started changing.
> 
> delay is ... "ping time".  jitter is a measure of how much ping times
> differ to each other.

Right for delay. But no for jitter. Jitter is, unless I remember wrong, 
comparison between your local clock and the server clock, and how much 
they are shifting around compared to each other. It has nothing to do 
with ping times.

And jitter have to get low for ntp to start syncing, since it's not 
possible to do any kind of syncing if local time is moving around too 
much compared to server time. It becomes impossible to tell how local 
time should be modified in such a case.

> It is kind of unreasonable that the jitter changes so much while delay
> seems to be always in the same region.

I would disagree.

>> ntp starts out with an interval of 64s, and backs off to 1024 eventuall,
>> over time, if things are stable. In this case things aren't stable, but it
>> seems to never have locked on to anything. So it's just been drifting the
>> whole time, it looks to me.
> 
> That's why I was interested in how the pll freq changed. The 1024sec
> poll interval however is an indicator for a successful lock.

No. It's an indication that ntp just don't see a need for more frequent 
polling. Which could either be because you have a lock, and all is 
stable, or you don't have a lock, and you are not going to achieve one 
based on information available. Primarily constantly way too high 
jitter. But I could be confused. It's a very long time since I was 
reading up on ntp, and most I can recall now are based on observations 
how ntp have been behaving on multiple systems over many years.

   Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: [email protected]             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol