| Re: [chrony-users] Possible bug in PPS support |
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Bill Unruh wrote:
On Mon, 23 Oct 2017, Miroslav Lichvar wrote:
On Mon, Oct 23, 2017 at 10:24:54AM -0700, Bill Unruh wrote:
On Mon, 23 Oct 2017, Rob Janssen wrote:
You don't support my calculation that if the clock apparently wandered
away 3400us
Again, no evidence of that 3400 us.
If I understand it correctly, 3.4ms was the offset of the NTP source
My question is how he determined that the offset was 3.4 ms after 13 hours. Simply looking at the offset from the one of the ntp servers does not cut it.
That is only 2 std dev from the mean.
I pasted the output for a single server but the other 2 were within very short offset of that:
MS Name/IP address Stratum Poll Reach LastRx Last sample
===============================================================================
#* PPS 0 4 0 13h -279ns[ -401ns] +/- 79ns
^- xxxxxx.xxxx.xxx 1 10 377 17m +3476us[+3476us] +/- 9930us
^- xxxxxx.xxxx.xxx 1 10 377 250 +3462us[+3462us] +/- 10ms
^- xxx.xxxxxx.xxxx.xxx 1 10 377 299 +3459us[+3459us] +/- 10ms
I am confident that those offsets were correct, but as I mentioned I forgot to subtract the offset that
was already there when the PPS sync was present (due to network delay asymmetry).
So that part of his concern is certainly valid. On the other hand, being
worried about the loss of connectivity on the 15 min time scale probably is
not, unless he has evidence.
But the evidence is all there in the measurement logs when the pps is running.
He could use that to estimate what the skew is over a variety of time periods.
Again, I am not interested in the performance when the clock is free-running as I do not believe
that it is good enough for our application anyway.
I am interested in monitoring/detecting that the clock is not synced to (recent) PPS input.
Rob
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