On Dec 3, 2019, at 12:20 PM, Jerry Geis <jerry.geis at gmail.com> wrote: > > int flag = 1; > if(setsockopt(fd, IPPROTO_TCP, TCP_NODELAY, &flag, sizeof(flag)) < 0) So first, I said “don’t do that,” and then you went and did that. :) But second, I’m guessing you did this on the receiving side, where it has no effect under any conditions. The Angle algorithm is about delaying the first packet on the sender’s side in anticipation of shortly receiving more data that can go in the same packet. Additionally, Nagle’s algorithm only works when there’s unacknowledged data, not on the first packet out on a new conn. Now that we’ve dispensed with Nagle, let’s get down to the actual issue.