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<h3>
Eric S. Raymond 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/4b5766702dab21aac310a990729cb5f86eafc20d">4b576670</a></strong>
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<span>by Eric S. Raymond</span>
<i>at 2017-06-11T07:55:39-04:00</i>
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<pre class="commit-message" style="margin: 0; white-space: pre-wrap">An observation about performance.
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<h4>1 changed file:</h4>
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<a href="#7bb1ded6cb62df2554422eb291b61743d3759964">
devel/tour.txt
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<h4>Changes:</h4>
<li id="7bb1ded6cb62df2554422eb291b61743d3759964">
<a href="https://gitlab.com/NTPsec/ntpsec/commit/4b5766702dab21aac310a990729cb5f86eafc20d#7bb1ded6cb62df2554422eb291b61743d3759964"><strong>devel/tour.txt</strong></a>
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<td class="diff-line-num unfold js-unfold old_line" data-linenumber="171" style="background: #fafafa; border-right-color: #f0f0f0; border-right-style: solid; border-right-width: 1px; color: rgba(0,0,0,0.3); padding: 0 5px; text-align: right; width: 35px" align="right" bgcolor="#fafafa">...</td>
<td class="diff-line-num unfold js-unfold new_line" data-linenumber="171" style="background: #fafafa; border-right-color: #f0f0f0; border-right-style: solid; border-right-width: 1px; color: rgba(0,0,0,0.3); padding: 0 5px; text-align: right; width: 35px" align="right" bgcolor="#fafafa">...</td>
<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">@@ -171,6 +171,16 @@ at protocol handling, packets arriving faster than the main loop could</td>
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<pre style="margin: 0"> <span id="LC171" class="line" lang="plaintext">cycle would pile up in the ring buffer and latecomers would be</span>
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<pre style="margin: 0"> <span id="LC172" class="line" lang="plaintext">dropped.</span>
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<pre style="margin: 0"> <span id="LC173" class="line" lang="plaintext"></span>
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<pre style="margin: 0">+<span id="LC174" class="line" lang="plaintext">(Also, it turns out not to be important at post-Y2K machine speeds to</span>
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<pre style="margin: 0">+<span id="LC175" class="line" lang="plaintext">get those arrival timestamps from the UDP layer ASAP, rather than</span>
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<pre style="margin: 0">+<span id="LC176" class="line" lang="plaintext">looking at packet read time in userspace. The cost of the latter,</span>
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<pre style="margin: 0">+<span id="LC177" class="line" lang="plaintext">naive approach is additional jitter dominated by process-scheduling</span>
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<pre style="margin: 0">+<span id="LC178" class="line" lang="plaintext">time. This used to be significant relative to users' accuracy</span>
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<pre style="margin: 0">+<span id="LC179" class="line" lang="plaintext">expectations for NTP, but scheduler timeslices have since decreased</span>
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<pre style="margin: 0">+<span id="LC180" class="line" lang="plaintext">by orders of magnitude and squashed the issue. We know this from some</span>
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<pre style="margin: 0">+<span id="LC181" class="line" lang="plaintext">tests setup having run for six months with packet-timestamp fetching</span>
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<pre style="margin: 0">+<span id="LC182" class="line" lang="plaintext">accidentally disabled...)</span>
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<pre style="margin: 0">+<span id="LC183" class="line" lang="plaintext"></span>
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<pre style="margin: 0"> <span id="LC184" class="line" lang="plaintext">The new organization stops pretending; it simply spins on a select</span>
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<pre style="margin: 0"> <span id="LC185" class="line" lang="plaintext">across all interfaces. If inbound traffic is more than the daemon can</span>
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<pre style="margin: 0"> <span id="LC186" class="line" lang="plaintext">handle, packets will pile up in the UDP layer and be dropped at that</span>
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