[ROS2] topic hz provides wrong rate for larger msgs
While testing the ros2_intel_realsense package on ROS eloquent (Ubuntu 18.04, ROS middleware FastRTPS) I realized, that ros2 topic hz reports far lower rates for a pointcloud2 topic than an explicit C++ subscriber.
The rgbd point cloud has about 5MB/frame and is published at 30Hz.
C++ subscriber:
[INFO] [pointcloud2_subscriber]: Recived 27 messages in 1.00 s (27.00 Hz)
[INFO] [pointcloud2_subscriber]: Recived 28 messages in 1.00 s (28.00 Hz)
[INFO] [pointcloud2_subscriber]: Recived 30 messages in 1.00 s (30.00 Hz)
[INFO] [pointcloud2_subscriber]: Recived 27 messages in 1.00 s (27.00 Hz)
ros2 topic hz:
average rate: 12.106
min: 0.022s max: 0.641s std dev: 0.09745s window: 100
average rate: 11.019
min: 0.022s max: 0.641s std dev: 0.10628s window: 100
average rate: 10.903
min: 0.022s max: 0.641s std dev: 0.10630s window: 100
average rate: 11.917
min: 0.022s max: 0.572s std dev: 0.09033s window: 100
This difference is quite significant.
Moreover, ros2 topic hzseems to cause a considerable load on the system, so that the rate of the C++ subscriber drops from ~25Hz to ~15Hz (ros2 topic hz drops to about 8Hz in this case).
As ros2 topic hz is written in python I also tried setting PYTHONOPTIMIZE=0 as suggested here, however with no effect on the results.
For comparison reasons, I tested a similar setup with ROS(1) melodic, where rostopic hz provides accurate and stable results.
Which leads me to the following questions:
- What could cause this significant difference of the measured rates? (related to QoS settings?)
- Is it possible to improve the performance of
ros2 topic hzin some way? - What is the recommended way of measuring rates of larger messages such as point clouds or images in ros2?
ros2 topic hzcausing an unexpected load on the system and outputing a seemingly lower/bad rate is "known." I thought I had seen work being done on it in the past 6 months, but I can't find anything. Not sure what can be done though. It might be worth opening a bug and see what the maintainers say: https://github.com/ros2/ros2cli/issues@christophebedard thank you very much for your reply. It is good to know, that I am not the only one facing this issue and that this is not caused by my specific setup/configuration. I will go forward and open an Issue on GitHub as you suggested.
Hello, the subscriber "pointcloud2", was it developed by you or does it already exist in a package? I need to subscribe to a topic to get the message rate, but without using the "ros2 topic HZ" command due to its latency.
@Bruno Arieira
pointcloud2_subscriberis just a simple C++ subscriber that increments a counter whenever a new message is received with an additional timer callback that logs the number of received messages in a given time interval. It was actually very similar to the Simple Cpp Publisher and Subscriber Tutorial (which also includes a timer in the publisher) except that I additionally specified the required QoS when creating the publisher.It was meant just as a quick comparison to
topic hz. Depending on your use case you might need something more advanced (e.g. include filtering etc.)