[Git][NTPsec/ntpsec][master] An observation about performance.

Eric S. Raymond gitlab at mg.gitlab.com
Sun Jun 11 11:55:51 UTC 2017

Eric S. Raymond pushed to branch master at NTPsec / ntpsec

4b576670 by Eric S. Raymond at 2017-06-11T07:55:39-04:00
An observation about performance.

- - - - -

1 changed file:

- devel/tour.txt


--- a/devel/tour.txt
+++ b/devel/tour.txt
@@ -171,6 +171,16 @@ at protocol handling, packets arriving faster than the main loop could
 cycle would pile up in the ring buffer and latecomers would be
+(Also, it turns out not to be important at post-Y2K machine speeds to
+get those arrival timestamps from the UDP layer ASAP, rather than
+looking at packet read time in userspace. The cost of the latter,
+naive approach is additional jitter dominated by process-scheduling
+time.  This used to be significant relative to users' accuracy
+expectations for NTP, but scheduler timeslices have since decreased
+by orders of magnitude and squashed the issue. We know this from some
+tests setup having run for six months with packet-timestamp fetching
+accidentally disabled...)
 The new organization stops pretending; it simply spins on a select
 across all interfaces.  If inbound traffic is more than the daemon can
 handle, packets will pile up in the UDP layer and be dropped at that

View it on GitLab: https://gitlab.com/NTPsec/ntpsec/commit/4b5766702dab21aac310a990729cb5f86eafc20d

View it on GitLab: https://gitlab.com/NTPsec/ntpsec/commit/4b5766702dab21aac310a990729cb5f86eafc20d
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