Messages in this thread Patch in this message | | | From | Benoit Sigoure <> | Subject | [PATCH] tcp: Lower the initial RTO to 1s as per draft RFC 2988bis-02. | Date | Wed, 18 May 2011 23:36:16 -0700 |
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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
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