[lttng-dev] Using lttng 2.11 and UST doesn't appear to work - getting empty trace files

Brian Hutchinson b.hutchman at gmail.com
Mon Apr 24 09:48:29 EDT 2023


Hi,

I'm on an embedded platform, i.MX8 using Lttng 2.11 with 5.6.69 kernel.

Tracing kernel events with lttng works fine but userspace (tracef and trace
provider type tracing) appears to have an issue I can't figure out.

systemd is starting up my application ( a bunch of processes and threads on
multiple cpu's) on boot.

I'm statically compiling and linking in lttng-ust.  If I use just tracef
type tracing, when I do lttng list --userspace I get nothing.  If I add in
a trace provider and a tracepoint, then I see my trace provider tracepoint
and:

     lttng_ust_tracelog:TRACE_DEBUG (loglevel: TRACE_DEBUG (14)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_LINE (loglevel: TRACE_DEBUG_LINE (13))
(type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_FUNCTION (loglevel:
TRACE_DEBUG_FUNCTION (12)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_UNIT (loglevel: TRACE_DEBUG_UNIT (11))
(type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_MODULE (loglevel: TRACE_DEBUG_MODULE
(10)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_PROCESS (loglevel: TRACE_DEBUG_PROCESS
(9)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_PROGRAM (loglevel: TRACE_DEBUG_PROGRAM
(8)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_DEBUG_SYSTEM (loglevel: TRACE_DEBUG_SYSTEM
(7)) (type: tracepoint)
     lttng_ust_tracelog:TRACE_INFO (loglevel: TRACE_INFO (6)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_NOTICE (loglevel: TRACE_NOTICE (5)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_WARNING (loglevel: TRACE_WARNING (4)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_ERR (loglevel: TRACE_ERR (3)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_CRIT (loglevel: TRACE_CRIT (2)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_ALERT (loglevel: TRACE_ALERT (1)) (type:
tracepoint)
     lttng_ust_tracelog:TRACE_EMERG (loglevel: TRACE_EMERG (0)) (type:
tracepoint)
     lttng_ust_tracef:event (loglevel: TRACE_DEBUG (14)) (type: tracepoint)
     lttng_ust_lib:unload (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_lib:debug_link (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_lib:build_id (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_lib:load (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_statedump:end (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_statedump:debug_link (loglevel: TRACE_DEBUG_LINE (13))
(type: tracepoint)
     lttng_ust_statedump:build_id (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_statedump:bin_info (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)
     lttng_ust_statedump:start (loglevel: TRACE_DEBUG_LINE (13)) (type:
tracepoint)

When I do lttng start, I get a directory structure in the trace directory
but the file sizes do not ever increase.  It's just a directory structure
with files created and then that's it, no events being written to the
files.  At first I thought things just weren't linked in right and not
working but then discovered how to run lttng-sessiond in -vvv mode and then
could see lots of things are going on, tracing appears to be trying to work
as there is tons of activity being output by lttng-sessiond, but like I
said the trace files aren't being added to.

I looked at the lttng-sessiond log I captured and can't quite make out the
problem so attaching it.

I'm probably not doing something right but can't figure out what that is so
any pointers appreciated.

Regards,

Brian
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