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tcp: add tcp_rto_max_ms sysctl 

Previous patch added a TCP_RTO_MAX_MS socket option
to tune a TCP socket max RTO value.

Many setups prefer to change a per netns sysctl.

This patch adds /proc/sys/net/ipv4/tcp_rto_max_ms

Its initial value is 120000 (120 seconds).

Keep in mind that a decrease of tcp_rto_max_ms
means shorter overall timeouts, unless tcp_retries2
sysctl is increased.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Eric Dumazet 2025-02-07 15:28:30 +00:00 committed by Paolo Abeni
parent 54a378f434
commit 1280c26228
6 changed files with 29 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
Documentation/networking/ip-sysctl.rst
View File

@ -705,6 +705,8 @@ tcp_retries2 - INTEGER
seconds and is a lower bound for the effective timeout.
TCP will effectively time out at the first RTO which exceeds the
hypothetical timeout.
If tcp_rto_max_ms is decreased, it is recommended to also
change tcp_retries2.
RFC 1122 recommends at least 100 seconds for the timeout,
which corresponds to a value of at least 8.
@ -1237,6 +1239,17 @@ tcp_rto_min_us - INTEGER
Default: 200000
tcp_rto_max_ms - INTEGER
Maximal TCP retransmission timeout (in ms).
Note that TCP_RTO_MAX_MS socket option has higher precedence.
When changing tcp_rto_max_ms, it is important to understand
that tcp_retries2 might need a change.
Possible Values: 1000 - 120,000
Default: 120,000
UDP variables
=============

1
Documentation/networking/net_cachelines/netns_ipv4_sysctl.rst
View File

@ -86,6 +86,7 @@ u8 sysctl_tcp_sack
u8 sysctl_tcp_window_scaling tcp_syn_options,tcp_parse_options
u8 sysctl_tcp_timestamps
u8 sysctl_tcp_early_retrans read_mostly tcp_schedule_loss_probe(tcp_write_xmit)
u32 sysctl_tcp_rto_max_ms
u8 sysctl_tcp_recovery tcp_fastretrans_alert
u8 sysctl_tcp_thin_linear_timeouts tcp_retrans_timer(on_thin_streams)
u8 sysctl_tcp_slow_start_after_idle unlikely(tcp_cwnd_validate-network-not-starved)

1
include/net/netns/ipv4.h
View File

@ -181,6 +181,7 @@ struct netns_ipv4 {
u8 sysctl_tcp_window_scaling;
u8 sysctl_tcp_timestamps;
int sysctl_tcp_rto_min_us;
int sysctl_tcp_rto_max_ms;
u8 sysctl_tcp_recovery;
u8 sysctl_tcp_thin_linear_timeouts;
u8 sysctl_tcp_slow_start_after_idle;

10
net/ipv4/sysctl_net_ipv4.c
View File

@ -28,6 +28,7 @@ static int tcp_adv_win_scale_max = 31;
static int tcp_app_win_max = 31;
static int tcp_min_snd_mss_min = TCP_MIN_SND_MSS;
static int tcp_min_snd_mss_max = 65535;
static int tcp_rto_max_max = TCP_RTO_MAX_SEC * MSEC_PER_SEC;
static int ip_privileged_port_min;
static int ip_privileged_port_max = 65535;
static int ip_ttl_min = 1;
@ -1583,6 +1584,15 @@ static struct ctl_table ipv4_net_table[] = {
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ONE,
},
{
.procname = "tcp_rto_max_ms",
.data = &init_net.ipv4.sysctl_tcp_rto_max_ms,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = proc_dointvec_minmax,
.extra1 = SYSCTL_ONE_THOUSAND,
.extra2 = &tcp_rto_max_max,
},
};
static __net_init int ipv4_sysctl_init_net(struct net *net)

6
net/ipv4/tcp.c
View File

@ -423,7 +423,7 @@ void tcp_init_sock(struct sock *sk)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
int rto_min_us;
int rto_min_us, rto_max_ms;
tp->out_of_order_queue = RB_ROOT;
sk->tcp_rtx_queue = RB_ROOT;
@ -433,8 +433,8 @@ void tcp_init_sock(struct sock *sk)
icsk->icsk_rto = TCP_TIMEOUT_INIT;
/* Use a sysctl ? */
icsk->icsk_rto_max = TCP_RTO_MAX;
rto_max_ms = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rto_max_ms);
icsk->icsk_rto_max = msecs_to_jiffies(rto_max_ms);
rto_min_us = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rto_min_us);
icsk->icsk_rto_min = usecs_to_jiffies(rto_min_us);

1
net/ipv4/tcp_ipv4.c
View File

@ -3532,6 +3532,7 @@ static int __net_init tcp_sk_init(struct net *net)
net->ipv4.sysctl_tcp_pingpong_thresh = 1;
net->ipv4.sysctl_tcp_rto_min_us = jiffies_to_usecs(TCP_RTO_MIN);
net->ipv4.sysctl_tcp_rto_max_ms = TCP_RTO_MAX_SEC * MSEC_PER_SEC;
return 0;
}