set tcp_nodelay

[bitianyuan123]

Submit the tcpnodelay Configuration Switch

Performance Optimization:

The server sends the SSH2_MSG_CHANNEL_OPEN_CONFIRMATION message immediately after sending the public key information (SSH2_MSG_GLOBAL_REQUEST).However, the client does not need to send any message (the SSH2_MSG_CHANNEL_Open and SSH2_MSG_GLOBAL_REQUEST messages have been sent). Therefore, after the client receives the message, the kernel waits for 40 ms to send an ACK message(due to the Nagle's algorithm). As a result, the server kernel needs to wait until the ACK with a delay of 40 ms is received when sending SSH2_MSG_CHANNEL_OPEN_CONFIRMATION.

In fact, the client and server set the socket status to TCP_NODELAY after the channel is established (received).

We will set TCP_NODELAY in advance until after authentication is complete.
We can also add a configuration option. When users are sensitive to performance, TCP_NODELAY is set after the TCP connection between the server and client is established.

This modification results in a 20% performance improvement in frequent short-connection environments.
An SSH connection takes about 200 ms. Setting TCP_NODELAY can optimize the performance of 40 ms.

[bitianyuan123]

https://bugzilla.mindrot.org/show_bug.cgi?id=3768