Yo Fred! On Mon, 25 Sep 2017 16:55:30 -0700 (PDT) Fred Wright via devel <devel@ntpsec.org> wrote:
> PPS(2) is the counter-capture PPS source, and is the primary timing > reference. Can you explain a bit more about this source? How does this differ from the KPPS or PPS(TIOCMIWAIT) sources? > SHM(1) is the combined NMEA/PPS source from GPSD, which is > configured to use the interrupt-based PPS driver, and hence > illustrates the offset in the interrupt-based capture. Your SHM(1), on both your hosts, seem to not be very good. Are you using KPPS? Or just TIOCMWAIT? > Again, PPS(2) is the main timing reference, though it's listed as > 127.127.22.2 due to the lame partial translation table in ntpviz. What do you think ntpviz should do better? Just convert 127.127.22.C to PPS(X) ? That would be ann easy patch. > The actual time offsets are > visible in the loopstats graph and in the PPS(2) peer offset graph, > and are substantially smaller than the offsets in SHM(1). QED. Well, your much poorer than normal SHM(1) Standard Deviation casts doubt on your QED. > > Uh, that is not my experience. And I have more control over my > > temperature than I have over my interrupt latency. > > See above. And note that you can at least make the latency (as well > as the variation in latency) as small as possible by running the CPU > as fast as possible, rather than slowing it down for "thermal > stability". I always run my ntpd's with the perfomance governor. So not an issue for me. I get 'thermal stability' by controlling an external heater and use that to stabilize my test enclosure. Then for fine temp control I vary the CPU workload to stabilize the CPU temp. Prolly several reasons why my SHM(1) seems to have 40x less jitter than yours. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 Veritas liberabit vos. -- Quid est veritas? "If you can’t measure it, you can’t improve it." - Lord Kelvin
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