On Tue, May 03, 2022 at 02:26:21PM +0000, Oleg Obleukhov via Linuxptp-users wrote: > Hi team, > In large distributed networks very many factors can lead to a short term > spike in offset. Primarily network equipment without Transparent Clock > support (even on a single device).
PTP was designed for networks with constant delay. On switched networks that requires full on-path PTP support. If you don't have that, you should be looking at NTP or another protocol designed for networks with variable delays, where more effective filtering can be implemented. Of course, that doesn't mean linuxptp couldn't try to do better in these suboptimal conditions. The question is if it's in the scope of the project. As you seem to have found out, the main issue with the current design is that dropping samples can lead to servo instability. > Looking at ptp4l config I didn’t to find anything to overcome this situation > and ignore this 1 bad outlier. > I implemented a quick patch > https://gist.github.com/leoleovich/5a4dff7e089bd429c5d208d9276e1683 which can > mitigate this and it works very well: > Preventing unnecessary tuning of the servo for a short period of time by > using a padding technique (simply filling with previous values). That patch seems to be dropping the sample and there is a different output shown in the example. Is there a newer version of the patch you didn't publish? > The bottom line is - we need to find a way to ignore outliers in a locked > state where it’s not expected to have shot term large jumps in offset. > Please check this out and let me know if there is a better way to handle this > situation or if this patch can inspire any other ideas… If a spike filter needs to be implemented, I think it would better if the threshold was automatically adjusted based on the jitter. For an example, see the "Popcorn spike suppressor" in RFC5905 (NTPv4). -- Miroslav Lichvar _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
