feat(hesai_hw_interface): configure and check SO_RCVBUF automatically

[mojomex]

PR Type

• Improvement

Related Links

• the patch to transport_drivers

Description

High-bandwidth sensors such as the OT128 may experience packet loss due to the UDP socket's receive buffer being too small by default. This PR adds functionality to set and confirm that buffer size.

The buffer has to be set to a size that

1. is as small as possible to save memory
2. large enough to store all packets that arrive while the UDP receiver thread is not scheduled or has its callback running

For now, the chosen (hard-coded) size is 1500 B * 3600 = 5.4 MB, which is the MTU size (1500 B) times the maximum number of packets in one full scan of OT128.
The memory footprint is still 'kind of' small compared to the size of pointcloud buffers etc., so condition 1 is fulfilled for the moment. In the future, computing the optimal buffer size based on sensor bandwidth would be preferable.

Review Procedure

Setting rmem_default and rmem_max is done like: sudo sysctl -w net.core.rmem_default=123.

• Set rmem_default and rmem_max to a size smaller than 5.4 MB, e.g. 500000 for 500 KB. Nebula should refuse to launch with an error message telling you to increase rmem_max.
• Set rmem_default to a small size like above, and set rmem_max to a value greater than 5.4 MB, e.g. 1000000000 for 1 GB. Nebula should now run, set its socket's buffer size to 5.4 MB and there should be no packet loss.

For the easiest review experience, comment out all point filters in hesai_decoder.hpp and hard-code the points' distance to be a fixed value. That way, you will see a perfect circle and immediately notice any missing secitons.

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• Assign PR to reviewer

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• Commits are properly organized and messages are according to the guideline
• (Optional) Unit tests have been written for new behavior
• PR title describes the changes

Post-Review Checklist for the PR Author

PR Author should check the checkboxes below before merging.

• All open points are addressed and tracked via issues or tickets

CI Checks

• Build and test for PR: Required to pass before the merge.

[knzo25]

Left some small questions 🙏

[knzo25]

LGTM

[knzo25]

@mojomex