Dear rt-users, I was happily using kernel version 5.4.84-rt47 on this Celeron j4125 system (all power management and cpu frequency scaling disabled in bios) and it was working great. Worst case cyclictest latency was around 30 to 40 us depending on system load. Due to some USB fixes landing in 5.14 I went and tried upgrading my kernel. I started with 5.19-rt10 but something weird showed up: cyclictest reported _huge_ latencies on one of the four cores (thread 1 of cyclictest) of around 700 us. So I went back to my old kernel to make sure it really was the kernel and sure thing. The old kernel still had the nice 30 to 40 us worst case latencies I determined previously. So I went through some kernel versions: 5.19-rt10 has the problem 5.17.1-rt17 has the problem 5.16.2-rt19 does not have the problem So I would guess somewhere between 5.16.2-rt19 and 5.17.1-rt17 something horrible happened ;) Maybe interesting fact: It is always thread 1 of cyclictest that shows the large latency. The other threads are seemingly completely in-line with the expectation of 30 - 40 us. Here's my cyclictest command: sudo ./cyclictest -m -p 95 -S -M cyclictest at stable/v1.0 I would possibly be willing to git bisect the issue. But I am a little bit confused about how to go about that. What repo/tree would I precisely bisect (I am using the the patch tarballs from https://cdn.kernel.org/pub/linux/kernel/projects/rt/)? Kind regards, FPS -- https://fps.io
