From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuchung Cheng Subject: Re: [PATCH] tcp: Lower the initial RTO to 1s as per draft RFC 2988bis-02. Date: Thu, 19 May 2011 10:42:19 -0700 Message-ID: References: <20110519.014656.1735519603194773578.davem@davemloft.net> <1305786976-84532-1-git-send-email-tsunanet@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Benoit Sigoure , Hsiao-keng Jerry Chu To: Benoit Sigoure Return-path: In-Reply-To: <1305786976-84532-1-git-send-email-tsunanet@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org 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 w= rote: > > 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 fr= om > >> there. =A0And then maybe we can discuss having a runtime knob some= more > >> :-) > > > > Yeah why don't we do that :-) > > Alright, here we go. > > > =A0include/net/tcp.h =A0 =A0| =A0 =A05 ++++- > =A0net/ipv4/tcp_input.c | =A0 13 +++++++++---- > =A02 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 s= tate, int timeo); > =A0#endif > =A0#define TCP_RTO_MAX =A0 =A0((unsigned)(120*HZ)) > =A0#define TCP_RTO_MIN =A0 =A0((unsigned)(HZ/5)) > -#define TCP_TIMEOUT_INIT ((unsigned)(3*HZ)) =A0 =A0/* RFC 1122 initi= al RTO value =A0 */ > +/* The next 2 values come from Draft RFC 2988bis-02. */ > +#define TCP_TIMEOUT_INIT ((unsigned)(1*HZ)) =A0 =A0 =A0 =A0 =A0 =A0/= * initial RTO value =A0 =A0*/ > +#define TCP_TIMEOUT_INIT_FALLBACK ((unsigned)(3*HZ)) =A0 /* initial = RTO to fallback to when > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0* a timeout happens during = the 3WHS. =A0 */ > > =A0#define TCP_RESOURCE_PROBE_INTERVAL ((unsigned)(HZ/2U)) /* Maximal= interval between probes > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * 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) > =A0{ > =A0 =A0 =A0 =A0struct tcp_sock *tp =3D tcp_sk(sk); > =A0 =A0 =A0 =A0struct dst_entry *dst =3D __sk_dst_get(sk); > + =A0 =A0 =A0 /* If we had to retransmit anything during the 3WHS, us= e > + =A0 =A0 =A0 =A0* the initial fallback RTO as per draft RFC 2988bis-= 02. > + =A0 =A0 =A0 =A0*/ > + =A0 =A0 =A0 int init_rto =3D inet_csk(sk)->icsk_retransmits ? > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 TCP_TIMEOUT_INIT_FALLBACK : TCP_TIMEOUT= _INIT; > > =A0 =A0 =A0 =A0if (dst =3D=3D NULL) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto reset; > @@ -890,7 +895,7 @@ static void tcp_init_metrics(struct sock *sk) > =A0 =A0 =A0 =A0if (dst_metric(dst, RTAX_RTT) =3D=3D 0) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto reset; > > - =A0 =A0 =A0 if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (TCP_T= IMEOUT_INIT << 3)) > + =A0 =A0 =A0 if (!tp->srtt && dst_metric_rtt(dst, RTAX_RTT) < (init_= rto << 3)) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0goto reset; > > =A0 =A0 =A0 =A0/* Initial rtt is determined from SYN,SYN-ACK. > @@ -916,7 +921,7 @@ static void tcp_init_metrics(struct sock *sk) > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0tp->mdev_max =3D tp->rttvar =3D max(tp= ->mdev, tcp_rto_min(sk)); > =A0 =A0 =A0 =A0} > =A0 =A0 =A0 =A0tcp_set_rto(sk); > - =A0 =A0 =A0 if (inet_csk(sk)->icsk_rto < TCP_TIMEOUT_INIT && !tp->r= x_opt.saw_tstamp) { > + =A0 =A0 =A0 if (inet_csk(sk)->icsk_rto < init_rto && !tp->rx_opt.sa= w_tstamp) { > =A0reset: > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0/* Play conservative. If timestamps ar= e not > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 * supported, TCP will fail to recalcu= late correct > @@ -924,8 +929,8 @@ reset: > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 */ > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0if (!tp->rx_opt.saw_tstamp && tp->srtt= ) { > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0tp->srtt =3D 0; > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 tp->mdev =3D tp->mdev_m= ax =3D tp->rttvar =3D TCP_TIMEOUT_INIT; > - =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 inet_csk(sk)->icsk_rto = =3D TCP_TIMEOUT_INIT; > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 tp->mdev =3D tp->mdev_m= ax =3D tp->rttvar =3D init_rto; > + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 inet_csk(sk)->icsk_rto = =3D init_rto; > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0} > =A0 =A0 =A0 =A0} > =A0 =A0 =A0 =A0tp->snd_cwnd =3D 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 =A0http://vger.kernel.org/majordomo-info.html