The problem with abstraction is that in order to deterministically control performance, you have to break down all the walls of the abstraction anyway. If I'm n

The problem with abstraction is that in order to deterministically control performance, you have to break down all the walls of the abstraction anyway. If I'm not 100% confident that my compiler will optimize a vector op with SIMD, and I absolutely require SIMD performance, then I end up having to know the entire layer cake to be able to verify that it is doing exactly that. In most cases it isn't a bad thing at all. But a use case like a timekeeping daemon, where a single unexpected garbage collection pause could cause a world of problems, it most definitely is more pain than gain.