Significant capacity drop on loopback interface

Hello everyone, Recently, I used netperf to test the TCP performance on loopback interface on my 2 nodes, one is installed kernel 4.4.103 and the other is 3.12.61 netperf -l 100 -t TCP_RR netperf -l 100 -t TCP_RR -- -D In both cases, I see that the throughput on 4.4.103 is about just 1/2 in

SO_TCP_NODELAY implementation in TCP stack

Hello everyone, As I know we have a socket option SO_TCP_NODELAY to disable Nagle Algorithm, and I found it is implemented in TCP/IP stack at https://elixir.bootlin.com/linux/v4.4.90/source/net/ipv4/tcp.c#L2401 . However, I do not know where the source code the Nagle Algorithm is implemented in