QNX had this right decades ago. The microkernel has upper bounds on everything it does. There are only a few tens of thousands of lines of microkernel code. All the microkernel does is allocate memory, dispatch the CPU, and pass messages between processes. Everything else, including drivers and loggers, is in user space and can be preempted by higher priority threads.

The QNX kernel doesn't do anything with strings. No parsing, no formatting, no messages.

Linux suffers from being too bloated for real time. Millions of lines of kernel, all of which have to be made preemptable. It's the wrong architecture for real time. So it took two decades to try to fix this.