On Mon, Jun 12, 2023 at 12:24:19PM +0800, egg car wrote: > 5) not only the 4 ports on the same nic, any combination of ptp0~ptp9 results > the same. > > > Have gone through the phc2sys codes, find nothing reasonable that explains > this issue so far. > > I can see when the large jitter happens, the measured delay also varies a lot, > perhapse it's related to the pcie tranfication process?
Yes, it's related to PCIe delays. The problem is that the kernel doesn't provide an ioctl to measure offset between two PHCs, so phc2sys has to do it in user space using clock_gettime(), which doesn't work very well (large delay, jitter and asymmetry). For PHC vs system clock measurements there is an optimized path in the kernel which for most drivers limits the delay to a single PCIe read. If you need to synchronize multiple PHCs to each other, it's better to use one phc2sys instance to synchronize the system clock to the source PHC and then another phc2sys instance to synchronize the rest of PHCs to the system clock. -- Miroslav Lichvar _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
