Also note that, if you're using TCP, Nagle's algorithm will be turned on unless you specifically turn it off; this is explicitly designed to avoid sending very short packets, by buffering them into larger packets in the kernel network stack up until some timeout or a minimum threshold size is reached. (Protocols such as ssh and telnet turn it off for interactivity.) And if you're using UDP, there's no flow control at all; while packets won't be aggregated á la Nagle, the network stacks on the sending and receiving ends can do pretty much whatever they want with the individual packets. And in either case the socket buffer size is only the "last mile": there is no way to control what happens elsewhere, and in particular the interrupt-time received packet handling usually won't know even what socket is the target, much less what buffer size that socket has set.