[PATCH] tcp: Implement a two-level initial RTO as per draft RFC 2988bis-02.
From: Benoit Sigoure
Date: Wed May 18 2011 - 22:23:36 EST
Prior to this patch, Linux would always use 3 seconds (compile-time
constant) as the initial RTO. Draft RFC 2988bis-02 proposes to tune
this down to 1 second and, in case of a timeout during the TCP 3WHS,
revert the RTO back up to 3 seconds when data transmission begins.
This patch implements this behavior but retains default values for
the initial RTO of 3 seconds, instead of 1 second as is suggested
in the draft RFC. This way, in a default configuration, the behavior
of Linux's TCP is unchanged.
This patch also adds 2 knobs to tweak the initial RTO:
- tcp_initial_rto: initial RTO used during the 3WHS (default remains
unchanged: 3 seconds). This was previously a compile-time constant.
- tcp_initial_fallback_rto: the RTO to fallback to if a timeout occurs
during the 3WHS, with a default value of 3 seconds too, as per the
draft RFC.
Signed-off-by: Benoit Sigoure <tsunanet@xxxxxxxxx>
---
On Wed, May 18, 2011 at 12:52 PM, David Miller <davem@xxxxxxxxxxxxx> wrote:
> I'll just as easily accept right now a patch right now which lowers
> the initial RTO to 1 second and adds the 3 second RTO fallback.
Here's a first attempt at a patch that implements the behavior described in
the draft RFC. I only compiled it so far, if you would like to move forward
with this approach, I'll go ahead and test it on a real server.
I'm not sure whether COUNTER_TRIES in syncookies.c should be based off
sysctl_tcp_initial_rto or sysctl_tcp_initial_fallback_rto, if we're going
to take the first one down to 1s...
Documentation/networking/ip-sysctl.txt | 19 +++++++++++++++++++
include/net/tcp.h | 4 +++-
net/ipv4/syncookies.c | 2 +-
net/ipv4/sysctl_net_ipv4.c | 20 ++++++++++++++++++++
net/ipv4/tcp.c | 4 ++--
net/ipv4/tcp_input.c | 13 +++++++++----
net/ipv4/tcp_ipv4.c | 6 +++---
net/ipv4/tcp_minisocks.c | 6 +++---
net/ipv4/tcp_output.c | 2 +-
net/ipv4/tcp_timer.c | 10 ++++++----
net/ipv6/syncookies.c | 2 +-
net/ipv6/tcp_ipv6.c | 6 +++---
12 files changed, 71 insertions(+), 23 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index d3d653a..590042c 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -384,6 +384,25 @@ tcp_retries2 - INTEGER
RFC 1122 recommends at least 100 seconds for the timeout,
which corresponds to a value of at least 8.
+tcp_initial_rto - INTEGER
+ This value sets the initial retransmit timeout (in milliseconds),
+ that is how long the kernel will wait before retransmitting the
+ initial SYN packet.
+
+ RFC 1122 says that this SHOULD be 3000 milliseconds, which is the
+ default. Note that draft RFC 2988bis-02 says that this SHOULD be
+ 1000 milliseconds, which might become the default value in future
+ versions.
+
+tcp_initial_fallback_rto - INTEGER
+ This value sets the initial retransmit timeout (in milliseconds)
+ to use after completing a three-way handshake during which the
+ initial SYN packet had to be retransmitted after waiting for
+ tcp_initial_rto milliseconds.
+
+ Draft RFC 2988bis-02 says that this MUST be 3000 milliseconds,
+ which is the default.
+
tcp_rfc1337 - BOOLEAN
If set, the TCP stack behaves conforming to RFC1337. If unset,
we are not conforming to RFC, but prevent TCP TIME_WAIT
diff --git a/include/net/tcp.h b/include/net/tcp.h
index cda30ea..c974242 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -213,6 +213,8 @@ extern int sysctl_tcp_syn_retries;
extern int sysctl_tcp_synack_retries;
extern int sysctl_tcp_retries1;
extern int sysctl_tcp_retries2;
+extern int sysctl_tcp_initial_rto; /* in jiffies */
+extern int sysctl_tcp_initial_fallback_rto; /* in jiffies */
extern int sysctl_tcp_orphan_retries;
extern int sysctl_tcp_syncookies;
extern int sysctl_tcp_retrans_collapse;
@@ -295,7 +297,7 @@ static inline void tcp_synq_overflow(struct sock *sk)
static inline int tcp_synq_no_recent_overflow(const struct sock *sk)
{
unsigned long last_overflow = tcp_sk(sk)->rx_opt.ts_recent_stamp;
- return time_after(jiffies, last_overflow + TCP_TIMEOUT_INIT);
+ return time_after(jiffies, last_overflow + sysctl_tcp_initial_rto);
}
extern struct proto tcp_prot;
diff --git a/net/ipv4/syncookies.c b/net/ipv4/syncookies.c
index 8b44c6d..b035968 100644
--- a/net/ipv4/syncookies.c
+++ b/net/ipv4/syncookies.c
@@ -186,7 +186,7 @@ __u32 cookie_v4_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
* sysctl_tcp_retries1. It's a rather complicated formula (exponential
* backoff) to compute at runtime so it's currently hardcoded here.
*/
-#define COUNTER_TRIES 4
+#define COUNTER_TRIES (sysctl_tcp_initial_rto/HZ + 1)
/*
* Check if a ack sequence number is a valid syncookie.
* Return the decoded mss if it is, or 0 if not.
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 321e6e8..abe8cfc 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -30,6 +30,8 @@ static int tcp_adv_win_scale_min = -31;
static int tcp_adv_win_scale_max = 31;
static int ip_ttl_min = 1;
static int ip_ttl_max = 255;
+static int tcp_min_rto = TCP_RTO_MIN;
+static int tcp_max_rto = TCP_RTO_MAX;
/* Update system visible IP port range */
static void set_local_port_range(int range[2])
@@ -247,6 +249,24 @@ static struct ctl_table ipv4_table[] = {
.proc_handler = proc_dointvec
},
{
+ .procname = "tcp_initial_rto",
+ .data = &sysctl_tcp_initial_rto,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_ms_jiffies,
+ .extra1 = &tcp_min_rto,
+ .extra2 = &tcp_max_rto,
+ },
+ {
+ .procname = "tcp_initial_fallback_rto",
+ .data = &sysctl_tcp_initial_fallback_rto,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_ms_jiffies,
+ .extra1 = &tcp_min_rto,
+ .extra2 = &tcp_max_rto,
+ },
+ {
.procname = "tcp_fin_timeout",
.data = &sysctl_tcp_fin_timeout,
.maxlen = sizeof(int),
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index b22d450..e9e7c3f 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2352,7 +2352,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
case TCP_DEFER_ACCEPT:
/* Translate value in seconds to number of retransmits */
icsk->icsk_accept_queue.rskq_defer_accept =
- secs_to_retrans(val, TCP_TIMEOUT_INIT / HZ,
+ secs_to_retrans(val, sysctl_tcp_initial_rto / HZ,
TCP_RTO_MAX / HZ);
break;
@@ -2539,7 +2539,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
break;
case TCP_DEFER_ACCEPT:
val = retrans_to_secs(icsk->icsk_accept_queue.rskq_defer_accept,
- TCP_TIMEOUT_INIT / HZ, TCP_RTO_MAX / HZ);
+ sysctl_tcp_initial_rto / HZ, TCP_RTO_MAX / HZ);
break;
case TCP_WINDOW_CLAMP:
val = tp->window_clamp;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index bef9f04..513cf7a 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.
+ */
+ int init_rto = inet_csk(sk)->icsk_retransmits ?
+ sysctl_tcp_initial_fallback_rto : sysctl_tcp_initial_rto;
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);
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index f7e6c2c..21920e6 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1383,7 +1383,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
want_cookie)
goto drop_and_free;
- inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+ inet_csk_reqsk_queue_hash_add(sk, req, sysctl_tcp_initial_rto);
return 0;
drop_and_release:
@@ -1834,8 +1834,8 @@ static int tcp_v4_init_sock(struct sock *sk)
tcp_init_xmit_timers(sk);
tcp_prequeue_init(tp);
- icsk->icsk_rto = TCP_TIMEOUT_INIT;
- tp->mdev = TCP_TIMEOUT_INIT;
+ icsk->icsk_rto = sysctl_tcp_initial_rto;
+ tp->mdev = sysctl_tcp_initial_rto;
/* So many TCP implementations out there (incorrectly) count the
* initial SYN frame in their delayed-ACK and congestion control
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 80b1f80..c63ffa0 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -472,8 +472,8 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
tcp_init_wl(newtp, treq->rcv_isn);
newtp->srtt = 0;
- newtp->mdev = TCP_TIMEOUT_INIT;
- newicsk->icsk_rto = TCP_TIMEOUT_INIT;
+ newtp->mdev = sysctl_tcp_initial_rto;
+ newicsk->icsk_rto = sysctl_tcp_initial_rto;
newtp->packets_out = 0;
newtp->retrans_out = 0;
@@ -582,7 +582,7 @@ struct sock *tcp_check_req(struct sock *sk, struct sk_buff *skb,
* it can be estimated (approximately)
* from another data.
*/
- tmp_opt.ts_recent_stamp = get_seconds() - ((TCP_TIMEOUT_INIT/HZ)<<req->retrans);
+ tmp_opt.ts_recent_stamp = get_seconds() - ((sysctl_tcp_initial_rto/HZ)<<req->retrans);
paws_reject = tcp_paws_reject(&tmp_opt, th->rst);
}
}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 17388c7..e34b0f6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2599,7 +2599,7 @@ static void tcp_connect_init(struct sock *sk)
tp->rcv_wup = 0;
tp->copied_seq = 0;
- inet_csk(sk)->icsk_rto = TCP_TIMEOUT_INIT;
+ inet_csk(sk)->icsk_rto = sysctl_tcp_initial_rto;
inet_csk(sk)->icsk_retransmits = 0;
tcp_clear_retrans(tp);
}
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index ecd44b0..47fa600 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -29,6 +29,8 @@ int sysctl_tcp_keepalive_probes __read_mostly = TCP_KEEPALIVE_PROBES;
int sysctl_tcp_keepalive_intvl __read_mostly = TCP_KEEPALIVE_INTVL;
int sysctl_tcp_retries1 __read_mostly = TCP_RETR1;
int sysctl_tcp_retries2 __read_mostly = TCP_RETR2;
+int sysctl_tcp_initial_rto __read_mostly = TCP_TIMEOUT_INIT;
+int sysctl_tcp_initial_fallback_rto __read_mostly = TCP_TIMEOUT_INIT;
int sysctl_tcp_orphan_retries __read_mostly;
int sysctl_tcp_thin_linear_timeouts __read_mostly;
@@ -135,8 +137,8 @@ static void tcp_mtu_probing(struct inet_connection_sock *icsk, struct sock *sk)
/* This function calculates a "timeout" which is equivalent to the timeout of a
* TCP connection after "boundary" unsuccessful, exponentially backed-off
- * retransmissions with an initial RTO of TCP_RTO_MIN or TCP_TIMEOUT_INIT if
- * syn_set flag is set.
+ * retransmissions with an initial RTO of TCP_RTO_MIN or
+ * sysctl_tcp_initial_rto if syn_set flag is set.
*/
static bool retransmits_timed_out(struct sock *sk,
unsigned int boundary,
@@ -144,7 +146,7 @@ static bool retransmits_timed_out(struct sock *sk,
bool syn_set)
{
unsigned int linear_backoff_thresh, start_ts;
- unsigned int rto_base = syn_set ? TCP_TIMEOUT_INIT : TCP_RTO_MIN;
+ unsigned int rto_base = syn_set ? sysctl_tcp_initial_rto : TCP_RTO_MIN;
if (!inet_csk(sk)->icsk_retransmits)
return false;
@@ -495,7 +497,7 @@ out_unlock:
static void tcp_synack_timer(struct sock *sk)
{
inet_csk_reqsk_queue_prune(sk, TCP_SYNQ_INTERVAL,
- TCP_TIMEOUT_INIT, TCP_RTO_MAX);
+ sysctl_tcp_initial_rto, TCP_RTO_MAX);
}
void tcp_syn_ack_timeout(struct sock *sk, struct request_sock *req)
diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c
index 352c260..f8a07a8 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -45,7 +45,7 @@ static __u16 const msstab[] = {
* sysctl_tcp_retries1. It's a rather complicated formula (exponential
* backoff) to compute at runtime so it's currently hardcoded here.
*/
-#define COUNTER_TRIES 4
+#define COUNTER_TRIES (sysctl_tcp_initial_rto/HZ + 1)
static inline struct sock *get_cookie_sock(struct sock *sk, struct sk_buff *skb,
struct request_sock *req,
diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index 4f49e5d..7e791e6 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -1349,7 +1349,7 @@ have_isn:
want_cookie)
goto drop_and_free;
- inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);
+ inet6_csk_reqsk_queue_hash_add(sk, req, sysctl_tcp_initial_rto);
return 0;
drop_and_release:
@@ -1957,8 +1957,8 @@ static int tcp_v6_init_sock(struct sock *sk)
tcp_init_xmit_timers(sk);
tcp_prequeue_init(tp);
- icsk->icsk_rto = TCP_TIMEOUT_INIT;
- tp->mdev = TCP_TIMEOUT_INIT;
+ icsk->icsk_rto = sysctl_tcp_initial_rto;
+ tp->mdev = sysctl_tcp_initial_rto;
/* So many TCP implementations out there (incorrectly) count the
* initial SYN frame in their delayed-ACK and congestion control
--
1.7.0.4
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