Hi. I'm running a 10us control loop by (under vxWorks) setting one thread's priority to max and not yielding ever (letting other tasks run on other cores), but Linux seems to thwart that capability: Ubuntu swaps out my thread occasionally for hundreds of microseconds; Yocto prints a "[sched_delayed] sched: RT throttling activated" message as soon as I start my thread, so it seems likely that it will swap out my thread periodically (I'm not quite able to confirm that yet), and even the fastest thread swap that I've heard of is too slow.
I tried changing the kernel's Preemption Model to "No Forced Preemption (Server)", but that didn't remove the RT throttling message. I browsed the rest of menuconfig but nothing looked related. I read an article from 2008 that talked about the kernel reserving 5% of the CPU for non-SCHED_FIFO tasks, so that's the direction and terminology I looked for in menuconfig. So maybe disabling RT throttling is all I need to do, maybe some other approach is needed. Hopefully someone will know more than I do. Thanks! Dave Mulder
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