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>

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 95feffb..d07c0dc 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -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);
-       }
+       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);