+++ /dev/null
----
-id: viewing-and-analyzing-your-traces
----
-
-This section describes how to visualize the data gathered after tracing
-the Linux kernel or a user space application.
-
-Many ways exist to read LTTng traces:
-
- * **`babeltrace`** is a command line utility which converts trace formats;
- it supports the format used by LTTng,
- <abbr title="Common Trace Format">CTF</abbr>, as well as a basic
- text output which may be `grep`ed. The `babeltrace` command is
- part of the
- <a href="http://diamon.org/babeltrace" class="ext">Babeltrace</a> project.
- * Babeltrace also includes **Python bindings** so that you may
- easily open and read an LTTng trace with your own script, benefiting
- from the power of Python.
- * **<a href="http://tracecompass.org/" class="ext">Trace Compass</a>**
- is an Eclipse plugin used to visualize and analyze various types of
- traces, including LTTng's. It also comes as a standalone application.
-
-LTTng trace files are recorded in the `~/lttng-traces` directory by default.
-Let's now view the trace and perform a basic analysis using
-`babeltrace`.
-
-The simplest way to list all the recorded events of a trace is to pass its
-path to `babeltrace` with no options:
-
-<pre class="term">
-babeltrace ~/lttng-traces/my-session
-</pre>
-
-`babeltrace` finds all traces recursively within the given path and
-prints all their events, merging them in order of time.
-
-Listing all the system calls of a Linux kernel trace with their arguments is
-easy with `babeltrace` and `grep`:
-
-<pre class="term">
-babeltrace ~/lttng-traces/my-kernel-session | grep sys_
-</pre>
-
-Counting events is also straightforward:
-
-<pre class="term">
-babeltrace ~/lttng-traces/my-kernel-session | grep sys_read | wc --lines
-</pre>
-
-The text output of `babeltrace` is useful for isolating events by simple
-matching using `grep` and similar utilities. However, more elaborate filters
-such as keeping only events with a field value falling within a specific range
-are not trivial to write using a shell. Moreover, reductions and even the
-most basic computations involving multiple events are virtually impossible
-to implement.
-
-Fortunately, Babeltrace ships with Python 3 bindings which makes it
-really easy to read the events of an LTTng trace sequentially and compute
-the desired information.
-
-Here's a simple example using the Babeltrace Python bindings. The following
-script accepts an LTTng Linux kernel trace path as its first argument and
-prints the short names of the top 5 running processes on CPU 0 during the
-whole trace:
-
-~~~ python
-import sys
-from collections import Counter
-import babeltrace
-
-
-def top5proc():
- if len(sys.argv) != 2:
- msg = 'Usage: python {} TRACEPATH'.format(sys.argv[0])
- raise ValueError(msg)
-
- # a trace collection holds one to many traces
- col = babeltrace.TraceCollection()
-
- # add the trace provided by the user
- # (LTTng traces always have the 'ctf' format)
- if col.add_trace(sys.argv[1], 'ctf') is None:
- raise RuntimeError('Cannot add trace')
-
- # this counter dict will hold execution times:
- #
- # task command name -> total execution time (ns)
- exec_times = Counter()
-
- # this holds the last `sched_switch` timestamp
- last_ts = None
-
- # iterate events
- for event in col.events:
- # keep only `sched_switch` events
- if event.name != 'sched_switch':
- continue
-
- # keep only events which happened on CPU 0
- if event['cpu_id'] != 0:
- continue
-
- # event timestamp
- cur_ts = event.timestamp
-
- if last_ts is None:
- # we start here
- last_ts = cur_ts
-
- # previous task command (short) name
- prev_comm = event['prev_comm']
-
- # initialize entry in our dict if not yet done
- if prev_comm not in exec_times:
- exec_times[prev_comm] = 0
-
- # compute previous command execution time
- diff = cur_ts - last_ts
-
- # update execution time of this command
- exec_times[prev_comm] += diff
-
- # update last timestamp
- last_ts = cur_ts
-
- # display top 10
- for name, ns in exec_times.most_common(5):
- s = ns / 1000000000
- print('{:20}{} s'.format(name, s))
-
-
-if __name__ == '__main__':
- top5proc()
-~~~
-
-Save this script as `top5proc.py` and run it with Python 3, providing the
-path to an LTTng Linux kernel trace as the first argument:
-
-<pre class="term">
-python3 top5proc.py ~/lttng-sessions/my-session-.../kernel
-</pre>
-
-Make sure the path you provide is the directory containing actual trace
-files (`channel0_0`, `metadata`, and the rest): the `babeltrace` utility
-recurses directories, but the Python bindings do not.
-
-Here's an example of output:
-
-~~~ text
-swapper/0 48.607245889 s
-chromium 7.192738188 s
-pavucontrol 0.709894415 s
-Compositor 0.660867933 s
-Xorg.bin 0.616753786 s
-~~~
-
-Note that `swapper/0` is the "idle" process of CPU 0 on Linux; since we
-weren't using the CPU that much when tracing, its first position in the list
-makes sense.
projects / lttng-docs.git / blobdiff