Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
Facebook is now using Chrony, you can read about their implementation: Building a more accurate time service at Facebook scale https://engineering.fb.com/production-engineering/ntp-service/ ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
On 2020-10-21, Miroslav Lichvar wrote: > On 2020-10-21, William Unruh wrote: >> On 2020-10-21, CRasch Net wrote: >>> Facebook is now using Chrony, you can read about their implementation: >>> >>> Building a more accurate time service at Facebook scale >>> https://engineering.fb.com/production-engineering/ntp-service/ >> >> Interesting. While I agree that chrony is more precise, I think that >> their results for ntpd are worse than they should be. ntpd can >> certainly do better than 1ms scatter/accuracy (and chrony can do better >> than 100us.There is something weird about their network paths.) About 10 >> years I ran a number of tests of chrony vs ntpd. and got about a fctor >> of 3-10 better, not 100. Interrupt latency/clock reading for chrony gave >> about 1us fluctuations. > > It's not clear how ntpd and chrony were configured in their tests. The > ntpq/chronyc outputs show a poll of 6, which is too long for a highly > stable synchronization in a local network. If they were using the > default minpoll 6 and maxpoll 10, a factor of 100 would not surprise me. > ntpd doesn't adjusts its polling very well when it has stable > measurements, so it would be effectively comparing ntpd polling at 10 vs > chrony polling at 6. > >> I find this whole thing about leap second smoothing to be a real farce. >> Just let the step occur instead of delivering the wrong time for hours. >> Or if you want, run your clocks on TIA not UTC and make the leapsecond >> conversion in the interpretation as is done for timezones. Would anyone >> advise leap day smoothing every 4 years so that we do not have trouble >> with our calenders? > > Well, yes. The trouble is that there are applications that break on > backward step, they need synchronized clocks, and not all NTP clients > can be configured to make a consistent slew on the leap second. So, the > easiest way to fix this is to make a slew on the server and hide the > leap second from the clients. When you internally do this everywhere and > you want to provide a public NTP service, it's easier to just serve your > internal leap-smeared time. Easier. It is probably even easier to forget about ntp and just free run your server. "Easy" is not the purpose of serving ntp time. > ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
On 2020-10-21 05:47, William Unruh wrote: On 2020-10-21, CRasch Net wrote: Facebook is now using Chrony, you can read about their implementation: Building a more accurate time service at Facebook scale https://engineering.fb.com/production-engineering/ntp-service/ Interesting. While I agree that chrony is more precise, I think that their results for ntpd are worse than they should be. ntpd can certainly do better than 1ms scatter/accuracy (and chrony can do better than 100us.There is something weird about their network paths.) About 10 years I ran a number of tests of chrony vs ntpd. and got about a fctor of 3-10 better, not 100. Interrupt latency/clock reading for chrony gave about 1us fluctuations. I find this whole thing about leap second smoothing to be a real farce. Just let the step occur instead of delivering the wrong time for hours. Or if you want, run your clocks on TIA not UTC and make the leapsecond conversion in the interpretation as is done for timezones. Would anyone advise leap day smoothing every 4 years so that we do not have trouble with our calenders? Originally, that is what they did, they smeared the leap day over 2 solar days. For a smeared timescale, perhaps something could be created that distributes UT instead of UTC, it would need an input file with the same data used to transmit UT-UTC in the standard radio protocol (see the ITU-R standard for UTC). Plus some kind of NTP protocol change to let clients know that the data incorporates the astronomical wobble and may need polling at the right time to pick up the wobble. Enjoy Jakob -- Jakob Bohm, CIO, Partner, WiseMo A/S. https://www.wisemo.com Transformervej 29, 2860 Søborg, Denmark. Direct +45 31 13 16 10 This public discussion message is non-binding and may contain errors. WiseMo - Remote Service Management for PCs, Phones and Embedded ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
On 2020-10-21, William Unruh wrote: > On 2020-10-21, CRasch Net wrote: >> Facebook is now using Chrony, you can read about their implementation: >> >> Building a more accurate time service at Facebook scale >> https://engineering.fb.com/production-engineering/ntp-service/ > > Interesting. While I agree that chrony is more precise, I think that > their results for ntpd are worse than they should be. ntpd can > certainly do better than 1ms scatter/accuracy (and chrony can do better > than 100us.There is something weird about their network paths.) About 10 > years I ran a number of tests of chrony vs ntpd. and got about a fctor > of 3-10 better, not 100. Interrupt latency/clock reading for chrony gave > about 1us fluctuations. It's not clear how ntpd and chrony were configured in their tests. The ntpq/chronyc outputs show a poll of 6, which is too long for a highly stable synchronization in a local network. If they were using the default minpoll 6 and maxpoll 10, a factor of 100 would not surprise me. ntpd doesn't adjusts its polling very well when it has stable measurements, so it would be effectively comparing ntpd polling at 10 vs chrony polling at 6. > I find this whole thing about leap second smoothing to be a real farce. > Just let the step occur instead of delivering the wrong time for hours. > Or if you want, run your clocks on TIA not UTC and make the leapsecond > conversion in the interpretation as is done for timezones. Would anyone > advise leap day smoothing every 4 years so that we do not have trouble > with our calenders? Well, yes. The trouble is that there are applications that break on backward step, they need synchronized clocks, and not all NTP clients can be configured to make a consistent slew on the leap second. So, the easiest way to fix this is to make a slew on the server and hide the leap second from the clients. When you internally do this everywhere and you want to provide a public NTP service, it's easier to just serve your internal leap-smeared time. -- Miroslav Lichvar ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
On 2020-10-21, CRasch Net wrote: > Facebook is now using Chrony, you can read about their implementation: > > Building a more accurate time service at Facebook scale > https://engineering.fb.com/production-engineering/ntp-service/ Interesting. While I agree that chrony is more precise, I think that their results for ntpd are worse than they should be. ntpd can certainly do better than 1ms scatter/accuracy (and chrony can do better than 100us.There is something weird about their network paths.) About 10 years I ran a number of tests of chrony vs ntpd. and got about a fctor of 3-10 better, not 100. Interrupt latency/clock reading for chrony gave about 1us fluctuations. I find this whole thing about leap second smoothing to be a real farce. Just let the step occur instead of delivering the wrong time for hours. Or if you want, run your clocks on TIA not UTC and make the leapsecond conversion in the interpretation as is done for timezones. Would anyone advise leap day smoothing every 4 years so that we do not have trouble with our calenders? ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
Re: [ntp:questions] How is the BIG guys (Google. FB etc) DNS and NTP architecture
rexon gaming wrote: Hi Folks, Searching for reference architecture of BIG players (Google, FB) for the DNS and NTP inside their data centers. If you have any please share. Google decided a few years ago to skip all leap seconds by implementing their own leap smear hack to a DMZ ntp server that bridges the gap between normal NTP servers and the internal "la, la, la, la, la, I can't hear you!" world which tries hard to avoid having to care about steps in UTC seconds counting. Terje -- - "almost all programming can be viewed as an exercise in caching" ___ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
