netdev - Re: SO_TCP_NODELAY implementation in TCP stack

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Date:   Mon, 02 Apr 2018 17:10:03 +0000
From:   Neal Cardwell <ncardwell@...gle.com>
To:     narutonguyen2018@...il.com
Cc:     Netdev <netdev@...r.kernel.org>
Subject: Re: SO_TCP_NODELAY implementation in TCP stack

On Sun, Apr 1, 2018 at 4:06 AM Naruto Nguyen <narutonguyen2018@...il.com>
wrote:

> 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 kernel. If you know, could you please help me?

The Linux TCP code for Nagle's algorithm is largely in tcp_output.c
in the following functions:

   tcp_nagle_check(), tcp_minshall_check(), tcp_minshall_update()

The variant of the Nagle algorithm that Linux implements is described here:

   https://tools.ietf.org/html/draft-minshall-nagle-00

Basically, the algorithm avoids having more than one outstanding
unacknowledged packet that is less than one MSS in size.

The Nagle algorithm is disabled using the TCP_NODELAY socket option.

neal