[PATCH] tcp: Lower the initial RTO to 1s as per draft RFC 2988bis-02.
From: Benoit Sigoure <hidden>
Date: 2011-05-19 06:37:25
Also in:
lkml
Subsystem:
networking [general], networking [tcp], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
From: Benoit Sigoure <redacted> 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 [off-list ref] wrote:
From: tsuna <redacted> Date: Wed, 18 May 2011 21:33:21 -0700quoted
On Wed, May 18, 2011 at 9:14 PM, David Miller [off-list ref] wrote:quoted
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);
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1.7.0.4