I have set up my real time kernel Preempt_RT ( 5.15.0-1063-realtime) with Ubuntu pro. When I run ping test, I always got high max latency at 1.5 to 4ms, which is not ok, it has to be less than 1ms because my robot runs at 1kHz. My average latency is quite good, about 0.1ms. I did a manual analysis and found that the latency will suddenly spikes up like that…

[1718410905.713206] 1208 bytes from icmp_seq=9460 ttl=64 time=0.124 ms

[1718410905.715765] 1208 bytes from icmp_seq=9461 ttl=64 time=1.66 ms

[1718410905.715953] 1208 bytes from icmp_seq=9462 ttl=64 time=0.177 ms

rtt min/avg/max/mdev = 0.087/0.145/2.588/0.078 ms

I have changed several cables, currently using a Cat8 cable, directly connecting the workstation PC to robot controller. Hyper-threading is disabled, CPU frequency scaled at ‘performance’, adjusted interrupt priority. My CPU is i7, computer Dell XPS8960. What could be the cause of the latency spike, or what could I try? I even disconnected the internet connection, so nothing is running, but it doesn't affect anything.

Thank you, would really appreciate any help! I have been stuck on this issue for two weeks now.



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