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<h3>
Gary E. Miller pushed to branch master
at <a href="https://gitlab.com/NTPsec/ntpsec">NTPsec / ntpsec</a>
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<h4>
Commits:
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<strong><a href="https://gitlab.com/NTPsec/ntpsec/commit/67c2abdabfea27bd84bdf934ba68bb40560dbcbe">67c2abda</a></strong>
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<span>by Gary E. Miller</span>
<i>at 2016-10-12T17:13:15-07:00</i>
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<pre class="commit-message" style="margin: 0; white-space: pre-wrap">ntpd: Fix another place good data being thrown away.
ntpd assumed that no refclock measurement could be more precise
that sys_precision. Measurements smaller than sys_precision were
replaced with sys_precision, even if the measure was zero or averaged.
This assumption is not valid when KPPS is used. The KPPS timestamps
can be much more precise than sys_precision. Sometimes more than 60%
of the good and precise data was being discarded.
Removing this bad code can be shown to decrease RMS Time Jitter
by a factor of 4 on a Raspberry Pi.
This problem became more obvious with Linux kernel 2.4.24 on RasPi.
This kernel degrades sys-precision from -20 to -19. That moved the
floor of RMS Time Jitter from 1 micro second to 2.
</pre>
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<h4>1 changed file:</h4>
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ntpd/ntp_loopfilter.c
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<h4>Changes:</h4>
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<a href="https://gitlab.com/NTPsec/ntpsec/commit/67c2abdabfea27bd84bdf934ba68bb40560dbcbe#diff-0"><strong>ntpd/ntp_loopfilter.c</strong></a>
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<td class="line_content match " style="background: #fafafa; color: rgba(0,0,0,0.3); padding-left: 0.5em; padding-right: 0.5em" bgcolor="#fafafa">@@ -667,10 +667,8 @@ local_clock(</td>
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<pre style="margin: 0"> <span id="LC667" class="line"><span class="cm" style="color: #998; font-style: italic"> * differences.</span></span>
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668
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668
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<pre style="margin: 0"> <span id="LC668" class="line"><span class="cm" style="color: #998; font-style: italic"> */</span></span>
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669
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669
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<pre style="margin: 0"> <span id="LC669" class="line"> <span class="n" style="color: #333">etemp</span> <span class="o" style="font-weight: bold">=</span> <span class="n" style="color: #333">SQUARE</span><span class="p">(</span><span class="n" style="color: #333">clock_jitter</span><span class="p">);</span></span>
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670
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<pre style="margin: 0"> <span id="LC670" class="line"> <span class="n" style="color: #333">dtemp</span> <span class="o" style="font-weight: bold">=</span> <span class="n" style="color: #333">SQUARE</span><span class="p">(</span><span class="n" style="color: #333">max</span><span class="p">(</span><span class="n" style="color: #333">fabs</span><span class="p">(</span><span class="n" style="color: #333">fp_offset</span> <span class="o" style="font-weight: bold">-</span> <span class="n" style="color: #333">last_offset</span><span class="p">),</span></span>
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671
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<pre style="margin: 0"> <span id="LC671" class="line"> <span class="n" style="color: #333">LOGTOD</span><span class="p">(</span><span class="n" style="color: #333">sys_precision</span><span class="p">)));</span></span>
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<pre style="margin: 0"> <span id="LC672" class="line"> <span class="n" style="color: #333">clock_jitter</span> <span class="o" style="font-weight: bold">=</span> <span class="n" style="color: #333">SQRT</span><span class="p">(</span><span class="n" style="color: #333">etemp</span> <span class="o" style="font-weight: bold">+</span> <span class="p">(</span><span class="n" style="color: #333">dtemp</span> <span class="o" style="font-weight: bold">-</span> <span class="n" style="color: #333">etemp</span><span class="p">)</span> <span class="o" style="font-weight: bold">/</span></span>
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673
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<pre style="margin: 0"> <span id="LC673" class="line"> <span class="n" style="color: #333">CLOCK_AVG</span><span class="p">);</span></span>
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<pre style="margin: 0"> <span id="LC670" class="line"> <span class="n" style="color: #333">dtemp</span> <span class="o" style="font-weight: bold">=</span> <span class="n" style="color: #333">SQUARE</span><span class="p">(</span><span class="n" style="color: #333">fp_offset</span> <span class="o" style="font-weight: bold">-</span> <span class="n" style="color: #333">last_offset</span><span class="p">);</span></span>
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<pre style="margin: 0"> <span id="LC671" class="line"> <span class="n" style="color: #333">clock_jitter</span> <span class="o" style="font-weight: bold">=</span> <span class="n" style="color: #333">SQRT</span><span class="p">(</span><span class="n" style="color: #333">etemp</span> <span class="o" style="font-weight: bold">+</span> <span class="p">(</span><span class="n" style="color: #333">dtemp</span> <span class="o" style="font-weight: bold">-</span> <span class="n" style="color: #333">etemp</span><span class="p">)</span> <span class="o" style="font-weight: bold">/</span> <span class="n" style="color: #333">CLOCK_AVG</span><span class="p">);</span></span>
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<pre style="margin: 0"> <span id="LC672" class="line"> <span class="k" style="font-weight: bold">switch</span> <span class="p">(</span><span class="n" style="color: #333">state</span><span class="p">)</span> <span class="p">{</span></span>
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<pre style="margin: 0"> <span id="LC674" class="line"> <span class="cm" style="color: #998; font-style: italic">/*</span></span>
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