[ssalin2]

What

Set TCP_NODELAY=1 on the SSH transport socket in SSHConnection._connect.

Why

paramiko leaves TCP_NODELAY unset, so the small exec-request and exit-status
packets each hit a TCP delayed-ACK stall (~40 ms) on every execute_command.
Disabling Nagle removes the stalls.

Measured (loopback SSH, network RTT ~0, so this is pure protocol overhead)

	per-command median
before (TCP_NODELAY=0)	89.9 ms
after (TCP_NODELAY=1)	49.6 ms (−44%)

Phase breakdown before the fix: exec_command ~43 ms + recv_exit_status ~45 ms
(the two Nagle/delayed-ACK round trips); open_session was only ~1.3 ms — i.e. the
cost was the stalls, not channel creation. On suites that issue thousands of commands
per test this is minutes of wall-clock savings.

Scope / safety

• Affects packet batching only — command execution, timeout handling, return codes
  and captured stdout/stderr are unchanged.
• Placed in _connect so it also applies after _reconnect().
• Guarded (transport is not None and transport.sock is not None) so it can't raise.
• import socket is stdlib; no new dependency.

Draft for review / to run CI. Happy to add a unit-test assertion that
setsockopt(IPPROTO_TCP, TCP_NODELAY, 1) is invoked on connect if desired.

[coveralls-official]

coverage: 80.839% (+0.01%) from 80.829% — ssalin2:perf/ssh-tcp-nodelay into intel:main

[adrianlasota]

I found one doubt. In case of using SSHConfigConnection with ProxyJump, transport.sock is a Paramiko Channel, not a native TCP socket. SSHConfigConnection._connect() passes the proxy channel via the sock argument, and Paramiko retains it as transport.sock.

Since Channel does not implement setsockopt(), it passes the None checks but raises AttributeError: 'Channel' object has no attribute 'setsockopt' here after successful authentication. This breaks initialization and reconnection for ProxyJump connections using the normal authentication path.

Could we restrict this optimization to native TCP sockets and add a regression test with a channel-backed transport? The existing test_connect_injects_sock_for_proxied mocks SSHConnection._connect(), so it does not exercise this new call.

[Copilot]

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Copilot review overview

2 open issues

• setsockopt() can raise (e.g., if the sock isn't a TCP socket, is already closed, or the… · New
• The comment claims the guard ensures this change 'can't raise', but that isn't accurate because… · New

What changed in this PR

Disables Nagle’s algorithm (sets TCP_NODELAY=1) on the Paramiko transport socket to reduce per-command SSH latency caused by delayed-ACK stalls.

Changes:

• Import stdlib socket to access TCP_NODELAY.
• After connecting, fetch Paramiko transport and set TCP_NODELAY on its underlying socket when available.

File	Description
mfd_connect/​ssh.py	Sets TCP_NODELAY on the SSH transport socket right after connect to improve command latency.

_{Review effort: Lite}