Hi everyone

I am experimenting with enabling trace for a specific iteration of a loop in my application.
I created 2 trace points at the start and end of the loop which log the iteration number.
the loop itself creates thousands of trace points. It runs for ~5ms.

on lttng side I created 2 triggers to start and stop my session in case the loop tracepoint registers a specific iteration number.
the triggers seem to work since there is another session entry created under the session folder but there are very few tracepoints.

is it possible that the delay between the event happening and the session trace starting causes loss of events ?
If yes, is there a way around this  ?

here is my setup :

#lttng-status
Recording session session: [inactive]

    Trace output: /home/user/lttng-traces/session-20230523-113537

=== Domain: User space ===

Buffering scheme: per-user

Tracked process attributes

  Virtual process IDs:  all

  Virtual user IDs:     all

  Virtual group IDs:    all

Channels:

-------------

- user-channel: [enabled]

    Attributes:

      Event-loss mode:  discard

      Sub-buffer size:  16777216 bytes

      Sub-buffer count: 128

      Switch timer:     inactive

      Read timer:       inactive

      Monitor timer:    1000000 us

      Blocking timeout: 0 us

      Trace file count: 1 per stream

      Trace file size:  unlimited

      Output mode:      mmap

    Statistics:

      Discarded events: 0

    Recording event rules:

      trace_events* (type: tracepoint) [enabled]

      loop* (type: tracepoint) [enabled]

#lttng list-triggers

- name: iter-start

  owner uid: 1000

  condition: event rule matches

    rule: loop:iteration (type: user tracepoint, filter: iter==2 && start == 1)

    errors: none

  actions:

    start session `session`

      errors: none

  errors: none

- name: iter-stop

  owner uid: 1000

  condition: event rule matches

    rule: loop:iteration (type: user tracepoint, filter: iter==2 && start == 0)

    errors: none

  actions:

    stop session `session`

      errors: none

  errors: none


Thanks

Yehuda