User space networking overlays impose a penalty just like and for much the same reason as dynamic language, garbage collection, etc. -- it's a trade-off between

User space networking overlays impose a penalty just like and for much the same reason as dynamic language, garbage collection, etc. -- it's a trade-off between versatility and performance. The best networking performance is achieved by binding directly to the metal using SOCK_RAW, but that also gives you the least flexibility.