Is that a bottleneck anymore? Maybe something that was appreciable in 1994 isn't a big performance hit in 2026?
I'm not sure this holds today. One example I can see is related to crypto. We used to have specific hardware for computing cryptography functions but it's now handled directly in standard hardware and the software has not evolved ( but it's been faster and faster to compute checksum functions )
Adding 20% to a 10 second operation is a lot longer on a wall clock than adding 20% to a 1 second operation.
If I could get a micro kernel with a better security profile than Linux, that doesn’t sound so bad. I could easily be using a ten year old chip for my day to day browsing and probably wouldn’t notice.
I suggest that you look at genode/sculpt:)
Making that fast is fundamental to any OS.
Most microkernals have methods to do IO in a different way. If they don't then likely they would pretty slow when doing I/O heavy operations.
Nginx is IO bound in general - for my headless go stateful server, i could get syscall6 up to 20% of the profile time. It was a fight between GC in the gRPC code allocating for headers and the syscall6 for top single profile footprint.