Hi there,
I am currently debugging a 2-step P2P_TC system that acts a bit
"strangely" (at least according to the current logic in linuxptp):
>From time to time, it delays follow-up messages and sends them not 1
sync message too late, but 2 sync messages too late (or more, in even
rarer cases).
ptp4l[11163.524]: port_syfufsm: SF_HAVE_SYNC: FUP_MATCH: seqid 17341
ptp4l[11163.549]: port_syfufsm: SF_EMPTY: SYNC_MISMATCH: new seqid 17342
ptp4l[11163.580]: port_syfufsm: SF_HAVE_SYNC: SYNC_MISMATCH:
last_syncfup seqid 17342 new seqid 17343
ptp4l[11163.612]: port_syfufsm: SF_HAVE_SYNC: SYNC_MISMATCH:
last_syncfup seqid 17343 new seqid 17344
ptp4l[11163.612]: process_follow_up: event FUP_MISMATCH, syfu
SF_HAVE_SYNC last sync fup seqid 17344, this fup seqid 17342
ptp4l[11163.612]: port_syfufsm: SF_HAVE_SYNC: FUP_MISMATCH:
last_syncfup seqid 17344 new seqid 17342
ptp4l[11163.643]: port_syfufsm: SF_HAVE_FUP: SYNC_MISMATCH:
last_syncfup seqid 17342 new seqid 17345
ptp4l[11163.644]: process_follow_up: event FUP_MISMATCH, syfu
SF_HAVE_SYNC last sync fup seqid 17345, this fup seqid 17343
ptp4l[11163.644]: port_syfufsm: SF_HAVE_SYNC: FUP_MISMATCH:
last_syncfup seqid 17345 new seqid 17343
ptp4l[11163.675]: port_syfufsm: SF_HAVE_FUP: SYNC_MISMATCH:
last_syncfup seqid 17343 new seqid 17346
This simple reordering throws off the ptp4l synchronization process
completely and irreversibly, as it only has the notion of a "last"
sync/fup message (history depth of 1).
I am a complete outsider when it comes to the linuxptp codebase, so I
figured it's best I asked first.
Should I go overboard and implement the history "the right way" (2
queues, one for sync, one for follow-up, each with tail dropping after
N seqids, and the FSM tries to iterate through the queues end-to-front
after each process_${msg}() function, in its attempt to consume
whatever seqid has completed in the meantime - meaning it has received
both its sync and fup)? Or is there some "shortcut" I can take to make
the synchronization at least recover from reordering?
Thanks,
-Vladimir
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