From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bill Fink Subject: Re: [PATCH 1/1] net: tcp: RTO restart Date: Wed, 19 Feb 2014 13:20:01 -0500 Message-ID: <20140219132001.12a9cf65.billfink@mindspring.com> References: <20140218181205.GA7780@kau.se> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, davem@davemloft.net, edumazet@google.com, anna.brunstrom@kau.se, apetlund@simula.no, michawe@ifi.uio.no, ilpo.jarvinen@helsinki.fi To: Per Hurtig Return-path: Received: from elasmtp-curtail.atl.sa.earthlink.net ([209.86.89.64]:50145 "EHLO elasmtp-curtail.atl.sa.earthlink.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754034AbaBSSUf (ORCPT ); Wed, 19 Feb 2014 13:20:35 -0500 In-Reply-To: <20140218181205.GA7780@kau.se> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, 18 Feb 2014, Per Hurtig wrote: > This patch implements the RTO restart modification described in > http://tools.ietf.org/html/draft-ietf-tcpm-rtorestart-02 > > RTO Restart's goal is to provide quicker loss recovery for segments lost in the > end of a burst/connection. To accomplish this the algorithm adjusts the RTO > value on each rearm of the retransmission timer to be exactly RTO ms after the > earliest outstanding segment was sent. The offsetting against the earliest > outstanding segment is not done by the regular rearm algorithm, which causes > RTOs to occur, on average, after RTO+RTT ms. > > As a faster timeout is only beneficial in scenarios where fast retransmit/early > retransmit cannot be triggered the algorithm will only kick in when there is a > small amount of outstanding segments. > > The RTO Restart proposal is accepted as a working group item in the IETF TCP > Maintenance and Minor Extensions (tcpm) TCP wg and is intended for experimental > RFC status. > > Signed-off-by: Per Hurtig > --- > include/net/tcp.h | 1 + > net/ipv4/sysctl_net_ipv4.c | 7 +++++++ > net/ipv4/tcp_input.c | 11 +++++++++++ > 3 files changed, 19 insertions(+) This should also have a documentation update to ip-sysctl.txt. A separate patch for the TCP(7) man page would also be useful if the kernel patch is approved. -Bill > diff --git a/include/net/tcp.h b/include/net/tcp.h > index 56fc366..575e82a 100644 > --- a/include/net/tcp.h > +++ b/include/net/tcp.h > @@ -278,6 +278,7 @@ extern int sysctl_tcp_slow_start_after_idle; > extern int sysctl_tcp_thin_linear_timeouts; > extern int sysctl_tcp_thin_dupack; > extern int sysctl_tcp_early_retrans; > +extern int sysctl_tcp_rto_restart; > extern int sysctl_tcp_limit_output_bytes; > extern int sysctl_tcp_challenge_ack_limit; > extern unsigned int sysctl_tcp_notsent_lowat; > diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c > index 44eba05..c605f4f 100644 > --- a/net/ipv4/sysctl_net_ipv4.c > +++ b/net/ipv4/sysctl_net_ipv4.c > @@ -717,6 +717,13 @@ static struct ctl_table ipv4_table[] = { > .extra2 = &four, > }, > { > + .procname = "tcp_rto_restart", > + .data = &sysctl_tcp_rto_restart, > + .maxlen = sizeof(int), > + .mode = 0644, > + .proc_handler = proc_dointvec, > + }, > + { > .procname = "tcp_min_tso_segs", > .data = &sysctl_tcp_min_tso_segs, > .maxlen = sizeof(int), > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index 227cba7..450ee30 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -98,6 +98,7 @@ int sysctl_tcp_thin_dupack __read_mostly; > > int sysctl_tcp_moderate_rcvbuf __read_mostly = 1; > int sysctl_tcp_early_retrans __read_mostly = 3; > +int sysctl_tcp_rto_restart __read_mostly = 1; > > #define FLAG_DATA 0x01 /* Incoming frame contained data. */ > #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a window update. */ > @@ -2972,6 +2973,16 @@ void tcp_rearm_rto(struct sock *sk) > */ > if (delta > 0) > rto = delta; > + } else if (icsk->icsk_pending == ICSK_TIME_RETRANS && > + sysctl_tcp_rto_restart && > + sk->sk_send_head == NULL && > + tp->packets_out < 4) { > + struct sk_buff *skb = tcp_write_queue_head(sk); > + const u32 rto_time_stamp = TCP_SKB_CB(skb)->when; > + s32 delta = (s32)(tcp_time_stamp - rto_time_stamp); > + > + if (delta > 0) > + rto -= delta; > } > inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, rto, > TCP_RTO_MAX); > -- > 1.7.9.5