UDP is little more than IP, so there isn't a technical reason why UDP couldn't be just as fast as TCP _per se_. But from when I was toying with writing a stream

UDP is little more than IP, so there isn't a technical reason why UDP couldn't be just as fast as TCP _per se_. But from when I was toying with writing a stream abstraction on top of UDP in Linux userspace, I came to the same conclusion, it's hard to achieve high throughput. My guess is that this is in part because achieving high throughput on IP is hard and in part because it's never going to be super efficient at this level (in userspace, on top of kernel infrastructure that might not be as optimized towards throughput like it is in the case of TCP).