That's always been true on MacOS, especially if you care about performance, are doing something weird, or both. I worked on OS-Bypass HPC drivers for a pre-inf

That's always been true on MacOS, especially if you care about performance, are doing something weird, or both. I worked on OS-Bypass HPC drivers for a pre-infiniband/ROCE NIC in the early/mid 2000s. About 90% of my time doing the driver was spent reading the kernel and IOKit sources, trying to figure out how I could use the highest performance interfaces possible in a stable way. For example, Apple really wanted you to use IOKit primitives (which used Mach IPC) to call functionality in your driver, but microbenchmarks showed it was about 50% higher latency than simple BSD ioctls from the BSD side of the kernel. That fit nicely with our driver model (which was split into OS-agnostic and OS specific code, and which used ioctls on every other *nix, and even on Windows), and got us slightly better performance.