Linux 5.15 + Ubuntu 22.04 real-time scheduling latency

[shuhaowu]

In the current chart, we see the worst-case scheduling latency is 60us, with the vast majority of the measurements to be below 50us. This test was conducted along with CPU stress (all four cores) for 2 hours. This represents a significant improvement from Kernel 5.4 on Ubuntu 20.04, where the worst case latency is >120us.

This is somewhat of a remarkable result, and I was asked about it ROScon 2022. To validate this, I've ran the same test for 24 hours and came to the same conclusions, which is good news:

• The worst case latency is 73 us (up from 60us measured previously)
• Out of the 1.7 billion measurements taken over the 24 hour period, only about 1000 measurements have scheduling latency values of over 50 us. This explains why I wasn't really able to observe these higher values over the 2 hour test.

73us remains to be a very low value and I believe the Raspberry Pi image we released remains an excellent platform for 1000 hz real-time applications.