The reordering issue reported by me initially on the linuxptp-devel list [0] with the sja1105 DSA driver turned out not to be a reordering issue at all, in fact.
Due to a kernel bug described in this patch [1], the DSA driver was in race with the master Ethernet driver and would occasionally (very rarely) deliver 2 TX timestamps to ptp4l on the event socket. The first TX timestamp is consumed in-band in the raw_send function. The second is caught by the main poll() syscall in the main ptp4l event loop - clock_poll(). When poll() sees the second TX-timestamped skb, it returns with revents == (POLLIN | POLLERR). But the main loop only checks for POLLIN, and says "yay, there's data!". So it proceeds to call recvmsg() with flags=0 (instead of MSG_ERRQUEUE), so it doesn't see any data in sk->sk_receive_queue. So, surprise, false alarm, the data that woke it up was in sk->sk_error_queue. The ptp4l process goes to sleep waiting for data. It sleeps for a whole sync interval. When it wakes up, it wakes up with the next sync, even though the previous sync's follow-up may have arrived in the meantime. Apparent reordering. Ptp4l does not print anything, it just appears to freeze. So this patch set aims to improves the error reporting in ptp4l, such that tracing back to the root cause is easier next time, and the problem does not blow up into other, completely unrelated things. [0]: https://sourceforge.net/p/linuxptp/mailman/message/36773629/ [1]: https://patchwork.ozlabs.org/patch/1210871/ Vladimir Oltean (3): ptp4l: Call recvmsg() with the MSG_DONTWAIT flag clock: Dump unexpected packets received on the error queues of sockets port: Signal sync/follow-up mismatch events loudly clock.c | 11 +++++++++++ msg.c | 12 ++++++++++++ msg.h | 7 +++++++ port.c | 21 +++++++++++++++++++++ raw.c | 2 +- udp.c | 2 +- udp6.c | 2 +- 7 files changed, 54 insertions(+), 3 deletions(-) -- 2.17.1 _______________________________________________ Linuxptp-devel mailing list Linuxptp-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
