Yo All! I have been chasing down an anomaly in the jitter data. See attached.
Before: peer-jitter-127.127.28.1-A.png After: peer-jitter-127.127.28.1-B.png You'll notice that all the data better than 0.954 µs is gone in the first plot. ntpd has been throwing away data that is 'too precise'! Gack! What does that mean for the numbers? There are a lot of small offsets that ntpd has been throwing away, so by not throwing them away, but instead using them, the std deviation of the 4 important metrics gets cut by about 25%. The 97% and 90% ranges get cut by about 10%. Not bad for a two line patch. I'll be pushing the basic patch today, and later I found several similar losses of 'precision' in the code. More on those later, but this appears to be the big win. Here are the raw numbers, before: Local Clock Time Offset Percentiles: Max: 21.312, 99%: 4.511, 95%: 1.327, 50%: -0.046, 5%: -1.319, 1%: -3.298, Min: -19.823 µs Ranges: 99% - 1% = 7.809 µs, 95% - 5% = 2.646 µs Deviation: Mean = 0.032 µs, 1σ = 1.307 µs Local Clock Frequency Offset Percentiles: Max: -6.438, 99%: -6.701, 95%: -7.038, 50%: -7.407, 5%: -8.175, 1%: -8.239, Min: -8.269 ppm Ranges: 99% - 1% = 1.538 ppm, 95% - 5% = 1.137 ppm Deviation: Mean = -7.504 ppm, 1σ = 0.353 ppm Peer Clock Offset: 127.127.28.1 Percentiles: Max: 21.313, 99%: 4.512, 95%: 1.328, 50%: -0.047, 5%: -1.320, 1%: -3.299, Min: -19.824 µs Ranges: 99% - 1% = 7.811 µs, 95% - 5% = 2.648 µs Deviation: Mean = 0.032 µs, 1σ = 1.308 µs Peer Clock Jitter: 127.127.28.1 Percentiles: Max: 19.992, 99%: 3.866, 95%: 2.157, 50%: 0.954, 5%: 0.954, 1%: 0.954, Min: 0.954 µs Ranges: 99% - 1% = 2.912 µs, 95% - 5% = 1.203 µs Deviation: Mean = 1.157 µs, 1σ = 0.630 µs After: Local Clock Time Offset Percentiles: Max: 6.075, 99%: 3.765, 95%: 1.203, 50%: -0.039, 5%: -1.192, 1%: -3.352, Min: -17.125 µs Ranges: 99% - 1% = 7.117 µs, 95% - 5% = 2.395 µs Deviation: Mean = -0.007 µs, 1σ = 0.992 µs Local Clock Frequency Offset Percentiles: Max: -5.903, 99%: -6.179, 95%: -6.490, 50%: -6.855, 5%: -7.339, 1%: -7.354, Min: -7.373 ppm Ranges: 99% - 1% = 1.175 ppm, 95% - 5% = 0.849 ppm Deviation: Mean = -6.892 ppm, 1σ = 0.298 ppm Peer Clock Offset: 127.127.28.1 Percentiles: Max: 6.075, 99%: 3.760s, 95%: 1.206, 50%: -0.037, 5%: -1.202, 1%: -3.353, Min: -17.126 µs Ranges: 99% - 1% = 7.113 µs, 95% - 5% = 2.408 µs Deviation: Mean = -0.006 µs, 1σ = 0.993 µs Peer Clock Jitter: 127.127.28.1 Percentiles: Max: 17.207, 99%: 3.633s, 95%: 2.170, 50%: 0.481, 5%: 0.151, 1%: 0.103, Min: 0.046 µs Ranges: 99% - 1% = 3.530 µs, 95% - 5% = 2.019 µs Deviation: Mean = 0.754 µs, 1σ = 0.767 µs RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588
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