From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sangtae Ha Subject: [PATCH 3/3] tcp_cubic: fix low utilization of CUBIC with HyStart Date: Sun, 13 Mar 2011 20:04:33 -0400 Message-ID: <1300061073-24209-1-git-send-email-sangtae.ha@gmail.com> Cc: Stephen Hemminger , David Miller , Injong Rhee , Bill Fink , , Sangtae Ha To: Lucas Nussbaum Return-path: Received: from mail-qy0-f181.google.com ([209.85.216.181]:51689 "EHLO mail-qy0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755565Ab1CNAEk (ORCPT ); Sun, 13 Mar 2011 20:04:40 -0400 Received: by qyg14 with SMTP id 14so3915569qyg.19 for ; Sun, 13 Mar 2011 17:04:40 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: HyStart sets the initial exit point of slow start. Suppose that HyStart exits at 0.5BDP in a BDP network and no history exists. If the BDP of a network is large, CUBIC's initial cwnd growth may be too conservative to utilize the link. CUBIC increases the cwnd 20% per RTT in this case. Signed-off-by: Sangtae Ha --- net/ipv4/tcp_cubic.c | 9 +++++++++ 1 files changed, 9 insertions(+), 0 deletions(-) diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index b758db1..a170778 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -270,6 +270,15 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd) ca->cnt = 100 * cwnd; /* very small increment*/ } + /* + * The initial growth of cubic function may be too conservative + * when the available bandwidth is still unknown. + */ + if (ca->loss_cwnd == 0) { + if (ca->cnt > 20) /* increase cwnd 5% per RTT */ + ca->cnt = 20; + } + /* TCP Friendly */ if (tcp_friendliness) { u32 scale = beta_scale; -- 1.7.0.4