From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: [PATCH] tcp: properly increase rcv_ssthresh for ofo packets Date: Fri, 06 Sep 2013 10:35:58 -0700 Message-ID: <1378488958.31445.47.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev , Neal Cardwell To: David Miller Return-path: Received: from mail-pb0-f52.google.com ([209.85.160.52]:56875 "EHLO mail-pb0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750708Ab3IFRf7 (ORCPT ); Fri, 6 Sep 2013 13:35:59 -0400 Received: by mail-pb0-f52.google.com with SMTP id wz12so3459070pbc.39 for ; Fri, 06 Sep 2013 10:35:59 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: From: Eric Dumazet TCP receive window handling is multi staged. A socket has a memory budget, static or dynamic, in sk_rcvbuf. Because we do not really know how this memory budget translates to a TCP window (payload), TCP announces a small initial window (about 20 MSS). When a packet is received, we increase TCP rcv_win depending on the payload/truesize ratio of this packet. Good citizen packets give a hint that it's reasonable to have rcv_win = sk_rcvbuf/2 This heuristic takes place in tcp_grow_window() Problem is : We currently call tcp_grow_window() only for in-order packets. This means that reorders or packet losses stop proper grow of rcv_win, and senders are unable to benefit from fast recovery, or proper reordering level detection. Really, a packet being stored in OFO queue is not a bad citizen. It should be part of the game as in-order packets. In our traces, we very often see sender is limited by linux small receive windows, even if linux hosts use autotuning (DRS) and should allow rcv_win to grow to ~3MB. Signed-off-by: Eric Dumazet Acked-by: Neal Cardwell --- net/ipv4/tcp_input.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 1969e16..28708d3 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4141,6 +4141,7 @@ static void tcp_data_queue_ofo(struct sock *sk, struct sk_buff *skb) if (!tcp_try_coalesce(sk, skb1, skb, &fragstolen)) { __skb_queue_after(&tp->out_of_order_queue, skb1, skb); } else { + tcp_grow_window(sk, skb); kfree_skb_partial(skb, fragstolen); skb = NULL; } @@ -4216,8 +4217,10 @@ add_sack: if (tcp_is_sack(tp)) tcp_sack_new_ofo_skb(sk, seq, end_seq); end: - if (skb) + if (skb) { + tcp_grow_window(sk, skb); skb_set_owner_r(skb, sk); + } } static int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen,