Messages in this thread | | | From | Yuchung Cheng <> | Date | Thu, 19 May 2011 10:42:19 -0700 | Subject | Re: [PATCH] tcp: Lower the initial RTO to 1s as per draft RFC 2988bis-02. |
| |
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 <tsunanet@gmail.com> wrote: > > From: Benoit Sigoure <tsuna@stumbleupon.com> > > 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 <davem@davemloft.net> wrote: > > From: tsuna <tsunanet@gmail.com> > > Date: Wed, 18 May 2011 21:33:21 -0700 > > > >> On Wed, May 18, 2011 at 9:14 PM, David Miller <davem@davemloft.net> 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/
| |