CPU overhead when discovery is used

[doisyg]

Description

Related to #1170
When recording a list of topics that are not all published, on a system with multiple topics, actions and services (typically a mobile robot with the nav2 stack), and with (default) automatic discovery, there is an important CPU usage from the bag recorder process.Typically 20% CPU usage on a very powerful machine (i7 13th gen)
We don't observe this CPU overhead with the same setup but --no-discovery added.

Expected Behavior

Reasonable CPU usage

Actual Behavior

Non reasonable CPU usage

System (please complete the following information)

• OS: Ubuntu 22.04
• ROS 2 Distro: Iron latest bin
• Install Method: apt
• Version: 0.22.3-1jammy.20230911.053809

[doisyg]

Update: no issue when using rosbag built from source and latest Iron commit: 7adc0f9
However when using source v0.22.3, the issue is there. So it feels that (good timing), the latest commit fix this issue.

Can you trigger a release ?

[fujitatomoya]

@doisyg i am not sure which commit actually fixes your problem here. but for releasing new packages would take some time.

CC: @Yadunund

[doisyg]

i am not sure which commit actually fixes your problem here. but for releasing new packages would take some time.

I am not sure myself but I know that I have the problem with v0.22.3 (even from source), and I don't with the latest version of the Iron branch (so probably these changes: 51a83f4)

What's blocking for releasing the latest Iron branch in the next sync ?

[MichaelOrlov]

@doisyg Yes, 51a83f4 might have improved the performance burden during discovery since we are deferring more heavy check to the end of the list when filtering out topics.

We will spawn a new release for iron, however as others mentioned it could take some time.
Meanwhile to workaround the issue you can explicitly specify a list of topics for the rosabg2 recorder. In this case, as soon as all topics are subscribed we are exiting from the rosbag2 discovery thread and there will not be extra burden on the performance.

[MichaelOrlov]

• Closing as fixed in the 51a83f4