From a performance point of view, the only difference between blocking and non-blocking I/O is the overall amount of state you need to find when an i/o is ready

From a performance point of view, the only difference between blocking and non-blocking I/O is the overall amount of state you need to find when an i/o is ready to complete (and how it is laid out in memory). For blocking I/O, the O/S needs to wake up a thread. For non-blocking I/O. the event loop returns with a handle being ready, which the user-level code needs to then look up to find the relevant buffer and control structures. For a benchmark (and some apps) it will come down to cpu cache misses on the loading the relevant state structures. For scaling (as opposed to 'speed'), it depends how 'cheap' your threads are (for blocking) and if your event loop etc can use multiple cores (for non-blocking).