It's kind of in User Space though - right? When an application opens a socket - it decides whether to open it with TCP_NODELAY or not. There isn't any kernel/os setting - it's done on a socket by socket basis, no?
TCP_NODELAY is implemented within the kernel. A socket can decide whether to use it or not.
TCP_NODELAY is implemented within the kernel. A socket can decide whether to use it or not.