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
# lttng set-session myothersession
-2) Enable event(s). Here for example, we want only 'sched_switch' and
-'sys_enter' events for the kernel (-k/--kernel).
+2) Enable all tracepoints and all system call events.
+
+# lttng enable-event -a -k
-# lttng enable-event sched_switch,sys_enter -k
+3) Enable tracepoint event(s). Here for example, we want only
+'sched_switch' and 'sched_wakeup' events for the kernel (-k/--kernel).
-or enable ALL events (-a/--all):
+# lttng enable-event sched_switch,sched_wakeup -k
-# lttng enable-event -a -k
+or enable ALL tracepoint events:
+
+# lttng enable-event -a -k --tracepoint
+
+4) Enable all system call event(s).
+
+# lttng enable-event -a -k --syscall
-3) Enable kprobes and/or the function tracer with lttng
+5) 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 -k --probe symbol+0x0
or
-# lttng enable-event aname --kprobe 0xffff7260695
+# lttng enable-event aname -k --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>
+# lttng enable-event aname -k --function <symbol_name>
-4) Enable context information for an event:
+6) Enable context information for an event:
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:
+7) 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.
-6) Start tracing:
+8) Start tracing:
# lttng start
Tracing is in progress at this point and traces will be written in
$HOME/lttng-traces/mysession-<date>-<time>
-7) Stop tracing:
+9) Stop tracing:
# lttng stop
Note: At this point, you can restart the trace (lttng start), enable/disable
events or just go take a break and come back 3 days later to start it again :).
-8) Destroy your session after you are done with tracing
+10) Destroy your session after you are done with tracing
# lttng destroy
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
+# babeltrace $HOME/lttng-traces/mysession-<date>-<time> | less
Voilà!
projects / lttng-tools.git / blobdiff