Plan

Plan for ROS 2 tracing & analysis effort.

Steps

This general effort will be split into a few distinct steps.

Instrumentation

The first goal is to statically instrument ROS 2, aiming for it to be in the ROS 2 E-turtle release (Nov 2019).

This includes transposing the existing ROS 1 instrumentation to ROS 2, wherever applicable. This step may not include instrumenting DDS implementations, and thus may be limited to the layer right before rmw.

The plan is to use LTTng with a ROS wrapper package like tracetools for ROS 1.

Analysis & visualization

After the initial instrumentation, some general statistics analyses can be built. The targeted analysis & visualization tools are pandas and Jupyter. The goal is to make analyses general enough to be useful for different use-cases, e.g.:

Callback duration
Time between callbacks (between two callback starts and/or a callback end and a start)
Message age (as the difference between processing time and message timestamp)
Message size
Memory usage
Execution time/proportion accross a process' nodes/components
Interruptions (noting that these may be more useful as time-based metrics instead of overall statistics):
- scheduling events during a callback
- delay between the moment a thread becomes ready and when it's actually scheduled
- CPU cycles

with mean, stdev, etc. when applicable.

Generic tracepoints should also be provided for ROS 2 user code, which could then be applied to a user-provided model for higher-level behaviour statistics.

Tools/accessibility

To make tracing ROS 2 more accessible and easier to adopt, we can put effort into integrating LTTng session setup & recording into the ROS 2 launch system.

This might include converting existing tracetools scripts to more flexible Python scripts, and then plugging that into the launch system.

ROS 1/2 compatibility

Finally, we could look into making analyses work on both ROS 1 and ROS 2, through a common instrumentation interface (or other abstraction).

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