"Terje Mathisen" <"terje.mathisen at tmsw.no"> wrote in message news:[email protected]... [] > NTP originally had 100ppm as the limit, with the intention that you'd > use the OS-level static adjustment call (which has a 100 ppm > granularity) to get it into the right neighborhood, i.e. within 50 ppm > worst case. > > NTP would then fine tune the clock the last 2-4 orders of magnitude to > lock onto the real UTC time.
Fine should the OS allow such adjustments. Some do not. I think it's a sign of NTP moving out of the lab and into a production/user environment that requirements like manual clock tweaking are dropped. >> if 500ppm includes 99.999% of computers it could be an excellent >> choice. > > This is probably approximately correct, i.e. with a population of many > thousand machines in our corporate network, I have _never_ seen a system > with a clock that has been off by more than 200-300 ppm. The exceptions > have always been due to driver issues (lost hardware interrupts) instead > of actual clock rate problems. That's a most helpful observation, Terje. >> As it is, in a community of end users perhaps one or two out of about a >> hundred have reported problems with NTP as supplied, and it seems a >> shame to exclude them if a small relaxation in the tolerance might >> allow them to run NTP rather than them having the view "NTP doesn't >> work". > > See above: This is almost certainly due to a sw rather than hw bug. It > was most often seen when people started using 1000 Hz clocks in Linux > instead of the old 100 Hz default. .. and the systems I now see with the poorest timekeeping are Vista and Windows-7 systems, which also have a 1KHz clock. I have also seen one particular piece of hardware & drivers have a very negative effect on timekeeping, supporting what you say. >> >> No chance of the limit being a command-line parameter, I suppose? > > It could be, it would mean turning a few core parameters in the control > loops into variables instead of constants. > > Terje I'm not holding my breathe for that, though. From what you have said, I am more of the opinion that 500ppm /is/ enough. Thanks, David _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
