This post is surprisingly shallow considering the author. I don't think it should be surprising to anyone even remotely familiar with low level programming that function calls have an overhead but inlining doesn't always always end up making things faster.

Inlining is also not a binary yes or no question. E.g. modern compilers can create clones of functions with constants propagated into some of the arguments, which gives some of the benefits of inlining. They are also free to change the calling convention (or make one up on the spot) for internal functions instead of inlining - something I'd like to see compilers explore further.