Commit c36207bd authored Apr 26, 2018 by Wei Wang Committed by David S. Miller Apr 27, 2018

tcp: remove mss check in tcp_select_initial_window()



In tcp_select_initial_window(), we only set rcv_wnd to
tcp_default_init_rwnd() if current mss > (1 << wscale). Otherwise,
rcv_wnd is kept at the full receive space of the socket which is a
value way larger than tcp_default_init_rwnd().
With larger initial rcv_wnd value, receive buffer autotuning logic
takes longer to kick in and increase the receive buffer.

In a TCP throughput test where receiver has rmem[2] set to 125MB
(wscale is 11), we see the connection gets recvbuf limited at the
beginning of the connection and gets less throughput overall.

Signed-off-by: Wei Wang <weiwan@google.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 448c907c

net/ipv4/tcp_output.c

+3 −5

Original line number	Diff line number	Diff line
		@@ -229,11 +229,9 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 mss,
		}
		}

		if (mss > (1 << *rcv_wscale)) {
		if (!init_rcv_wnd) /* Use default unless specified otherwise */
		init_rcv_wnd = tcp_default_init_rwnd(mss);
		rcv_wnd = min(rcv_wnd, init_rcv_wnd * mss);
		}

		/* Set the clamp no higher than max representable value */
		(window_clamp) = min_t(__u32, U16_MAX << (rcv_wscale), *window_clamp);