On Tue, Mar 05, 2019 at 08:25:17AM +0000, C. Devereaux wrote: > After reading more about that, instead of hardcoding an offset of 37 (and > keeping track of the when it must be changed) I decided to hardcode 0 > instead, and to run the ptp4l server in UTC, through either legacy hardware > timestamping or software timestamping.
Software timestamping is much less accurate and legacy timestamping is not supported in the mainline driver AFAIK. The UTC offset can be specified in the configuration, if for some reason 37 doesn't work for you. > Also, it takes some time to reach a smaller offset. I would like to “start > from scratch” and have the offset jump., ie make the NICs match the RTC > immediately, before starting to broadcast PTP messages. > > However, the -F to force step sync on start to do that seems to be ignored, > regardless of the units I use: The step will happen only in the s1 state. With a small I constant it takes up 1000 seconds to reach the s1 state, because it needs to measure the frequency offset very accurately. > For now, I’m using linreg in phc2sys (even if I can’t start from scratch, at > least it is adjusting faster), and software timestamping (in ptp4l, to get > UTC values ie -O0 offset) Yeah, that won't work very well. You need HW timestamping and a very slow servo. > There is no switch anywhere in my setup. All the NICs are connected directly > to eachother by crossover cables to minimize such issues. I just can’t have a > proper PTP grandmaster In the DC, so I’m trying to find work arounds: server > 1 in master mode, servers 2 and running running timemaster (slave mode) Why do you need PTP? If there are no switches, you could use NTP with HW timestamping and get a similar performance, except the configuration would be much simpler (no need for mixing PTP with NTP). > Is there anything I could do to take advantage the direct connection between > the NICs to further reduce jitter on server2 and 3? Is there any interest at > all in using L2? Or on using the direct connection between server 2 and > server 3 I don't think L2 will help, at least not with e1000e. The connection between server 2 and 3 could be useful if server 1 will not always be the grandmaster. But this would complicate the configuration quite a bit (it's not possible with timemaster). > Because another way to look at them is that the servers are hooked together > in a triangle > : > server1 (eth2) <-- server 2 (eth1) > server 1 (eth3) (eth3) > | ^ > V | > Server 3(eth1) | > Server 3 (eth2) ----/ Ok, so there are two interfaces on server 1. I missed that. I think you need one of them to be synchronized to the system clock (using very small PI constants) as I suggested before. The other interface needs to be synchronized to the first interface using default PI constants or linreg. ptp4l needs to be configured with the boundary_clock_jbod option. HTH, -- Miroslav Lichvar _______________________________________________ Linuxptp-users mailing list Linuxptp-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-users
