Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933758Ab1ESRmo (ORCPT ); Thu, 19 May 2011 13:42:44 -0400 Received: from smtp-out.google.com ([216.239.44.51]:24638 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933628Ab1ESRmm convert rfc822-to-8bit (ORCPT ); Thu, 19 May 2011 13:42:42 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=google.com; s=beta; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type:content-transfer-encoding; b=oZzRvy5aD/iTdOfdAq0kh4lfWkj0p8pzGa4wlIll2dr9kJcZiRzjPBvUsASofPIGad wKbiE4OG0PLRkXsC4xGg== MIME-Version: 1.0 In-Reply-To: <1305786976-84532-1-git-send-email-tsunanet@gmail.com> References: <20110519.014656.1735519603194773578.davem@davemloft.net> <1305786976-84532-1-git-send-email-tsunanet@gmail.com> From: Yuchung Cheng Date: Thu, 19 May 2011 10:42:19 -0700 Message-ID: Subject: Re: [PATCH] tcp: Lower the initial RTO to 1s as per draft RFC 2988bis-02. To: Benoit Sigoure Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Benoit Sigoure , Hsiao-keng Jerry Chu Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4676 Lines: 112 Hi Benoit, AFAICT, the passive open side would not fall back the RTO to 3sec in this change because SYNACK timeouts are not recorded in icsk_retransmits but reqsk->retrans? Yuchung On Wed, May 18, 2011 at 11:36 PM, Benoit Sigoure wrote: > > From: Benoit Sigoure > > Draft RFC 2988bis-02 recommends that the initial RTO be lowered > from 3 seconds down to 1 second, and that in case of a timeout > during the TCP 3WHS, the RTO should fallback to 3 seconds when > data transmission begins. > --- > > On Wed, May 18, 2011 at 10:46 PM, David Miller wrote: > > From: tsuna > > Date: Wed, 18 May 2011 21:33:21 -0700 > > > >> On Wed, May 18, 2011 at 9:14 PM, David Miller wrote: > >>> I really would rather see the initial RTO be static and be set to 1 > >>> with fallback RTO of 3. > >> > >> I can also provide a simple patch for this if you want to start from > >> there. ?And then maybe we can discuss having a runtime knob some more > >> :-) > > > > Yeah why don't we do that :-) > > Alright, here we go. > > > ?include/net/tcp.h ? ?| ? ?5 ++++- > ?net/ipv4/tcp_input.c | ? 13 +++++++++---- > ?2 files changed, 13 insertions(+), 5 deletions(-) > > diff --git a/include/net/tcp.h b/include/net/tcp.h > index cda30ea..274d761 100644 > --- a/include/net/tcp.h > +++ b/include/net/tcp.h > @@ -122,7 +122,10 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo); > ?#endif > ?#define TCP_RTO_MAX ? ?((unsigned)(120*HZ)) > ?#define TCP_RTO_MIN ? ?((unsigned)(HZ/5)) > -#define TCP_TIMEOUT_INIT ((unsigned)(3*HZ)) ? ?/* RFC 1122 initial RTO value ? */ > +/* The next 2 values come from Draft RFC 2988bis-02. */ > +#define TCP_TIMEOUT_INIT ((unsigned)(1*HZ)) ? ? ? ? ? ?/* initial RTO value ? ?*/ > +#define TCP_TIMEOUT_INIT_FALLBACK ((unsigned)(3*HZ)) ? /* initial RTO to fallback to when > + ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?* a timeout happens during the 3WHS. ? */ > > ?#define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal interval between probes > ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? * for local resources. > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c > index bef9f04..a36bc35 100644 > --- a/net/ipv4/tcp_input.c > +++ b/net/ipv4/tcp_input.c > @@ -868,6 +868,11 @@ static void tcp_init_metrics(struct sock *sk) > ?{ > ? ? ? ?struct tcp_sock *tp = tcp_sk(sk); > ? ? ? ?struct dst_entry *dst = __sk_dst_get(sk); > + ? ? ? /* If we had to retransmit anything during the 3WHS, use > + ? ? ? ?* the initial fallback RTO as per draft RFC 2988bis-02. > + ? ? ? ?*/ > + ? ? ? int init_rto = inet_csk(sk)->icsk_retransmits ? > + ? ? ? ? ? ? ? TCP_TIMEOUT_INIT_FALLBACK : TCP_TIMEOUT_INIT; > > ? ? ? ?if (dst == NULL) > ? ? ? ? ? ? ? ?goto reset; > @@ -890,7 +895,7 @@ static void tcp_init_metrics(struct sock *sk) > ? ? ? ?if (dst_metric(dst, RTAX_RTT) == 0) > ? ? ? ? ? ? ? ?goto reset; > > - ? ? ? if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_TIMEOUT_INIT << 3)) > + ? ? ? if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (init_rto << 3)) > ? ? ? ? ? ? ? ?goto reset; > > ? ? ? ?/* Initial rtt is determined from SYN,SYN-ACK. > @@ -916,7 +921,7 @@ static void tcp_init_metrics(struct sock *sk) > ? ? ? ? ? ? ? ?tp->mdev_max = tp->rttvar = max(tp->mdev, tcp_rto_min(sk)); > ? ? ? ?} > ? ? ? ?tcp_set_rto(sk); > - ? ? ? if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->rx_opt.saw_tstamp) { > + ? ? ? if (inet_csk(sk)->icsk_rto < init_rto && !tp->rx_opt.saw_tstamp) { > ?reset: > ? ? ? ? ? ? ? ?/* Play conservative. If timestamps are not > ? ? ? ? ? ? ? ? * supported, TCP will fail to recalculate correct > @@ -924,8 +929,8 @@ reset: > ? ? ? ? ? ? ? ? */ > ? ? ? ? ? ? ? ?if (!tp->rx_opt.saw_tstamp && tp->srtt) { > ? ? ? ? ? ? ? ? ? ? ? ?tp->srtt = 0; > - ? ? ? ? ? ? ? ? ? ? ? tp->mdev = tp->mdev_max = tp->rttvar = TCP_TIMEOUT_INIT; > - ? ? ? ? ? ? ? ? ? ? ? inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT; > + ? ? ? ? ? ? ? ? ? ? ? tp->mdev = tp->mdev_max = tp->rttvar = init_rto; > + ? ? ? ? ? ? ? ? ? ? ? inet_csk(sk)->icsk_rto = init_rto; > ? ? ? ? ? ? ? ?} > ? ? ? ?} > ? ? ? ?tp->snd_cwnd = tcp_init_cwnd(tp, dst); > -- > 1.7.0.4 > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at ?http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/