[ntp:questions] How to determin hardware latency for PPS offset given simple tools.

Paul G bodosom at gmail.com
Thu Jun 20 19:48:10 UTC 2013

On Tuesday, June 4, 2013 3:44:19 PM UTC-4, E-Mail Sent to this address will be added to the BlackLists wrote:
> Is interrupt coalescing disabled on the gigabit ethernet adapters?

Not by me. I assume when ntpq reports symmetric delays proportional to interface speed that interrupts are not the issue for my question.  Perhaps that's a poor assumption.

My question was -- given PPS clocks on the same network with ntpq offsets of:
0.021, 0.130, 0.064 and -0.046 -- any of which can be fudged away how do I determine the truth.  That is how much is (consistent) hardware latency of any sort versus algorithmic restriction.

e.g. delay, offset and jitter from two sides of a gigE connection:
0.073   -0.008   0.002
0.064    0.011   0.006

Likewise fastE:
1.226   -0.059   0.076
1.104    0.109   0.068

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