[ros-users] [Discourse.ros.org] [Next Generation ROS] Latency and throughput in ROS2

Anup Pemmaiah ros.discourse at gmail.com
Sat Sep 29 02:12:25 UTC 2018

Hi Victor,

Thank you for the reports related to latency using RT_PREMPT linux and ROS 2 with various network settings. It was very interesting to read.

Have couple of questions.

1) In the base RT_PREEMPT linux kernel report (https://arxiv.org/pdf/1808.10821.pdf), I understand Table-III and Table-IV is what matters. But, while looking at, Table-II (Roundtrip latency results with RT normal), was curious if you know what might be the reason for TX traffic at 100Mbps, the MAX latency is considerably high at 25ms? I would expect latency to be high when RX traffic at 100Mbps 

2) In the ROS 2 evaluation report (https://arxiv.org/pdf/1809.02595.pdf), in Fig 5-a, when the system is idle, DDS2 has high MAX latency(4ms) compared to others. Was just curious which DDS implementation is this and what might be the reason?

3)  In the Fog 6-f of the ROS 2 evaluation report, at 80Mbps, where it cannot meet the deadlines and dropped packets, was curious, is ksoftirqd processing the packets the primary cause for the latency or can it be the DDS layer causing the latency. Also, about packets being dropped, would setting the size of kernel socket buffers ( net.core.rmem*, net.core.wmem*) would help too. 


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