The overhead is really minimal. I happened to have an old program around that uses LuaJIT or Lua5.1. It calls a two functions that each increments a C int. Usin

The overhead is really minimal. I happened to have an old program around that uses LuaJIT or Lua5.1. It calls a two functions that each increments a C int. Using the FFI, calling this function 500 million times takes 0.7 seconds. Calling it as an old-style exported function takes 5.4 seconds for 500 million calls. Disabling the JIT increases the FFI time to 32.7s and decreases the old-style time to 4.7 seconds. On Lua5.1, calling the function takes 6.7s. This is in no way representative of any reach benchmark, but as you can see: Lua is pretty fast.