Marek, On 2021-01-06 09:06, Marek Dorsic wrote: > NTP has a drift file (usually /var/lib/ntp/ntp.drift or /var/lib/ntp/drift on > Linux) where it stores and periodically updates the computers clock drift > measured by ntpd in ppm. > In your scenario I assume it should contain only one number - 0. If it’s not > 0, does it correspond to the drift you are observing?
If the actual clock is more than 15 ppm off from the value in the drift file, it will never track in the frequency error. This is due to algorithm error in the NTPD. I have pointed out this problem, but there have been very little interest in fixing it. The tell-tale of this being the problem will be a continuous reset of the clock phase. While this may not be the issue for this particlar test, one should be careful. The existence of a drift file bypasses the frequency learning phase, and there is no recovery mechanism if the phase learning phase fails. Cheers, Magnus > > .md > >> On 6 Jan 2021, at 08:28, Hal Murray <hmur...@megapathdsl.net> wrote: >> >> >>> My question is: what i'm missing? >> Two ideas come to mind. >> >> Most PCs (and servers) smear the CPU clock frequency slightly to dance >> around >> the FCC rules. The chip that does that will have slight temperature >> influence >> so even if everything else is working right there will be tiny changes if >> you >> look closely enough. >> >> On Linux, you will see something like this at boot time. (look in dmesg) >> [ 0.000000] tsc: Detected 3292.448 MHz processor >> >> Even if the hardware does the right thing, the software may screwup. If >> your >> system is using the TSC for timekeeping, that number above is used to setup >> the conversion from TSC ticks to ns. A year or 6 ago, there was a bug in >> that >> routine. If you patched the boot code to call that routine a half dozen >> times >> you would get a half dozen different answers. The kernel guys didn't notice >> because they were all close enough that ntpd could compensate. But any geek >> looking at ntpd graphs of drift would notice big jumps when the system was >> rebooted. >> >> >> -- >> These are my opinions. I hate spam. >> >> >> >> >> _______________________________________________ >> time-nuts mailing list -- time-nuts@lists.febo.com >> To unsubscribe, go to >> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
