Hi all,
As I mentioned briefly in my thread "Wrong procname for userspace trace of app
with different thread names", I found that I had to do an 'enable-channel' step
to get UST context such as the thread name to actually appear in the trace.
>From further investigation, it appears that if I perform 'enable-event' before
>'add-context', that also makes the context appear. Here are three sequences
>of commands where I'm enabling the same UST context (vpid, vtid and procname)
>and same UST events (all) each time, but only the first sequence includes
>'enable-channel', and I switched around the order of 'add-context' and
>'enable-event' in the second and third. Note that in the second command
>sequence, the second set of curly braces - those containing the context - is
>missing from the 'lttng view' output.
Good: 'enable-channel' before 'add-context':
"""
# lttng create
Session auto-20121029-085910 created.
Traces will be written in /root/lttng-traces/auto-20121029-085910
# lttng enable-channel channel0 --userspace
UST channel channel0 enabled for session auto-20121029-085910
# lttng add-context --userspace -t vpid -t vtid -t procname
UST context procname added to all channels
UST context vtid added to all channels
UST context vpid added to all channels
# lttng enable-event --userspace --all
All UST events are enabled in channel channel0
# lttng start
Tracing started for session auto-20121029-085910
# lttng stop
Tracing stopped for session auto-20121029-085910
# lttng view
Trace directory: /root/lttng-traces/auto-20121029-085910
[09:00:34.022479500] (+?.?????????) mydaemon:13811 daemon:start: { cpu_id = 1
}, { procname = "mythread.9", vtid = 13993, vpid = 13811 }, { myvar = 999 }
[...]
# lttng destroy
Session auto-20121029-085910 destroyed at /root
"""
Bad: 'add-context' before 'enable-event':
"""
# lttng create
Session auto-20121029-090142 created.
Traces will be written in /root/lttng-traces/auto-20121029-090142
# lttng add-context --userspace -t vpid -t vtid -t procname
UST context procname added to all channels
UST context vtid added to all channels
UST context vpid added to all channels
# lttng enable-event --userspace --all
All UST events are enabled in channel channel0
# lttng start
Tracing started for session auto-20121029-090142
# lttng stop
Tracing stopped for session auto-20121029-090142
# lttng view
Trace directory: /root/lttng-traces/auto-20121029-090142
[09:02:11.520300500] (+?.?????????) mydaemon:13811 daemon:start: { cpu_id = 0
}, { myvar = 999 }
[...]
# lttng destroy
Session auto-20121029-090142 destroyed at /root
"""
Good: 'add-context' AFTER 'enable-event':
"""
# lttng create
Session auto-20121029-090738 created.
Traces will be written in /root/lttng-traces/auto-20121029-090738
# lttng enable-event --userspace --all
All UST events are enabled in channel channel0
# lttng add-context --userspace -t vpid -t vtid -t procname
UST context procname added to all channels
UST context vtid added to all channels
UST context vpid added to all channels
# lttng start
Tracing started for session auto-20121029-090738
# lttng stop
Tracing stopped for session auto-20121029-090738
# lttng view
Trace directory: /root/lttng-traces/auto-20121029-090738
[09:08:04.670574000] (+?.?????????) mydaemon:13811 daemon:start: { cpu_id = 1
}, { procname = "mythread.9", vtid = 13993, vpid = 13811 }, { myvar = 999 }
[...]
# lttng destroy
Session auto-20121029-090738 destroyed at /root
"""
I am using lttng-ust-2.0.5 which I have patched with commit 009745db "Cache the
procname per-thread rather than per-process to take into account that prctl()
can be used to set thread names.", lttng-tools-2.0.4 and babeltrace-1.0.0.rc5.
Thanks in advance,
David
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