How to trace non-ROS2 functions within ros2_tracing and view in tracecompass about ros2_tracing HOT 3 CLOSED

You can instrument your own code with LTTng and then use the ros2_tracing tools to enable the tracepoints (Trace action or ros2 trace command).

If you want to get a flame graph or flame chart for your functions, I'd recommend using gcc's function instrumentation feature (-finstrument-functions). This adds function calls at the start and end of the instrumented functions if you build with this option. You can use the instrument-functions mixin to do this with colcon (e.g., colcon build --packages-up-to your_package --mixin instrument-functions). gcc only allows you to instrument all functions and exclude individual functions or headers, so I'd recommend using this gcc plugin I've created in order to only instrument the individual functions you want: https://github.com/christophebedard/instrument-attribute-gcc-plugin. Then you can add __attribute__((instrument_function)) to your helper functions (specifically their definitions IIRC). You'll need to provide the flag with the path to the plugin to gcc through colcon, like this I think: colcon build --packages-up-to your_package --cmake-args "-DCMAKE_C_FLAGS='-finstrument-functions,-fplugin=/abs/path/to/instrument_attribute.so'" "-DCMAKE_CXX_FLAGS='-finstrument-functions,-fplugin=/abs/path/o/instrument_attribute.so'" (so you might as well skip using the mixin).

You can then use LTTng to trigger tracepoints inside the special functions that gcc adds: https://lttng.org/docs/v2.13/#doc-liblttng-ust-cyg-profile. You'll need to enable those special tracepoints (lttng_ust_cyg_profile*/lttng_ust_cyg_profile*:func_entry) like this: https://gitlab.com/ros-tracing/tracetools_analysis/-/blob/9c853b27fc380d763317ce786f0588007db8f33b/tracetools_analysis/launch/profile.launch.py#L29-L30. You also need to LD_PRELOAD LTTng's liblttng-ust-cyg-profile.so library (or liblttng-ust-cyg-profile-fast.so), but the Trace action or ros2 trace command should do that for you automatically when you tell it to enable the lttng_ust_cyg_profile*:func_* tracepoints.

Then you can import the trace into Trace Compass, and it should be able to display the information as a flame chart/graph, see: https://archive.eclipse.org/tracecompass/doc/stable/org.eclipse.tracecompass.doc.user/LTTng-UST-Analyses.html#Flame_Chart_View.

I've written code to use trace data generated from the standard ROS 2 instrumentation (i.e., from ros2_tracing) in Trace Compass (like Figures 4 and 5 in this paper). You could then compare the flame charts of your functions to your subscription/timer callbacks, etc., e.g., by looking at the results side by side in Trace Compass. However, this is not all easily available yet. You could try to build Trace Compass yourself if you (really) wanted to, see: https://github.com/christophebedard/ros2-message-flow-analysis#analysis. Eventually you'll be able to download Trace Compass and install this feature, though.

Otherwise, if you create your own instrumentation, then you'll need to do the data analysis yourself (using tracetools_anlaysis or by writing a custom Trace Compass plugin). This is why I recommend going the -finstrument-functions way for your use-case here.

Hope that's useful. Let me know if you have any questions!

from ros2_tracing.

Thanks for the detailed reply Christophe! Looks really useful.

It will take me some time to familiarize myself with the tools and try this out. I'll let you know if I have any questions, but feel free to close this issue in the meantime.

from ros2_tracing.

Sounds good!

from ros2_tracing.