[lttng-dev] background information about LTTng timestamps

[Sébastien Barthélémy]

Hello all,

I'm using LTTng 2 (only UST for now) to study the behaviour of a realtime
multiprocess application. Some of the traces I get suggest the synchronization
between the processes is not working as expected.

However this might ascome from latencies or even hops in LTTng clock source.
(Or maybe some bugs in the scripts I use to process the LTTng traces.)

Before digging deeper in our app synchronization mechanisms, I'd like
to get a better
understanding of the way LTTng timestamps my data, how accurate these timestamps
are and under which conditions I can trust them.

Is this covered somewhere? I had a look at the source code, but
without much success.
Where should I start?

I added tracepoints with the current time as argument and measured
that the LTTng
timestamps where only ~3us behind. Moreover this latency was the same across
the two processes so this connot account for the ~500us quirks I see.

Thank you (again) for any help

Best regards
-- Sébastien