tracing session is needed beforehand. To interact with the session daemon and a
tracing session, you should use the lttng command line UI (lttng).
-Here is a list of some new powerful features the LTTng 2.0 kernel tracer
-offers:
+Here is a list of some powerful features the LTTng 2.0 kernel tracer offers:
* Kprobes support
* Function Tracer support
* Context information support (add context data to an event)
* Perf counter support
+ * Tracepoint support
The next sections explain how to do tracing :)
Kernel Tracing
--------------
-You have to modprobe the lttng-modules manually or the session daemon will do
-it for you if those modules can be found on your system.
+You can start the session daemon by invoking the command "ltt-sessiond",
+or let the lttng command line tool do it for you. The session daemon
+loads the LTTng tracer modules for you if those modules can be found on
+your system. If they are not found, the kernel tracing feature will be
+unavailable.
-Again, you can then start the session daemon (ltt-sessiond) by hand or the
-lttng command line tool will do it for you.
-
-List possible kernel events:
+List available kernel events:
# lttng list -k
3) Enable kprobes and/or the function tracer with lttng
This is a new feature made possible by the new LTTng 2.0 kernel tracer. You can
-enable a Kprobe (by Masami Hiramatsu) and data will be output in the trace
-along side with your tracing data.
+enable a dynamic probe and data will be output in the trace along side with
+your tracing data.
-# lttng enable-event aname --kprobe symbol+0xffff7260695
+# lttng enable-event aname --probe symbol+0xffff7260695
or
-# lttng enable-event aname --kprobe 0xffff7260695
+# lttng enable-event aname --probe 0xffff7260695
-Either an <address> or a <symbol+offset> can be used for kprobes.
+Either an <address> or a <symbol+offset> can be used for probes.
-You can also enable function tracer, which uses the ftrace API (by Steven
+You can also enable function tracer, which uses the Ftrace API (by Steven
Rostedt). Again, data will be output in the trace.
# lttng enable-event aname --function <symbol_name>
This is also a new feature which allows you to add context information to an
event. For example, you can add the PID along with the event information:
-# lttng add-context -k -e sched_switch -t 0
+# lttng add-context -k -e sched_switch -t pid
At this point, you will have to look at 'lttng add-context --help' for all
possible context type which are integer values.
You can on the same line activate multiple context:
-# lttng add-context -k -e sched_switch -t 0 -t 2 -t 4
+# lttng add-context -k -e sched_switch -t pid -t nice -t tid
5) Enable perf counter for an event:
Again, a new powerful feature is the possibility to add perf counter data
-(using the perf API by Ingo Molnar) to the trace on a per event basis. Let say
-we want to get the CPU cycles at each define event:
+(using the perf API by Ingo Molnar and Thomas Gleixner) to the trace on a per
+event basis. Let say we want to get the CPU cycles at each event:
-# lttng add-context -k -e sched_switch -t 1 --perf-name aname --perf-type 0 --perf-id 0
+# lttng add-context -k -e sched_switch -t perf:cpu-cycles
You'll have to use the add-context help for all possible perf counter values.
Reading a trace
--------------
-To read your trace, you can use babeltrace which will text dump your the
-trace. Please see http://www.efficios.com/ctf and git tree
+The tool "Babeltrace" can be used to dump your binary trace into a
+human-readable text format. Please see
+http://www.efficios.com/babeltrace and git tree
http://git.efficios.com/?p=babeltrace.git
# babeltrace -n $HOME/lttng-traces/mysession-<date>-<time> | less
projects / lttng-tools.git / blobdiff