[ltt-dev] [LTTng-modules] [task] Timestamp after trace_mark

[david.mandoloni (LTTng Project)]

Issue status update for
http://lttng.org/issue/213
Post a follow up:
http://lttng.org/comment/reply/213#comment-form


  Project:      LTTng tracer modules
  Version:      0.19
  Component:    Code
  Category:     task
  Priority:     normal
  Assigned to:  Anonymous
  Status:       new
  Updated by:   david.mandoloni

Hi guys,


I'm currently studying the way through which lttng gets tracepoints
timestamp. Debugging the code in User Mode I've seen that, invoking
trace_mark function, a call like that
"(*__mark_##channel##_##name.call)" is done; this is marker_probe_cb(),
in kernel/marker.c . Then, inside, we have the calling to the probe
function associated, "func(mdata, mdata->single.probe_private,
call_private, mdata->format, &args)", but I haven't understood when, and
how, it gets time information.


An example:


"kernel.irq_entry: 0.751273193 (/trace/kernel_0), 943, 943, mmcqd, , 2,
0x0, IRQ { ip = 3225171396, handler = 0xc02aafc4, irq_id = 131,
kernel_mode = 1 }"


How the 0.751273193 value is retrieved?


Can you give me a "road" to understand that?


Thanks a lot,


David



david.mandoloni