[RFC 2/3] tcp: Use mtu probes if RACK is enabled
From: Leonard Crestez <hidden>
Date: 2021-05-11 12:04:50
Also in:
lkml
Subsystem:
documentation, networking [general], networking [tcp], the rest · Maintainers:
Jonathan Corbet, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Neal Cardwell, Linus Torvalds
RACK allows detecting a loss in min_rtt / 4 based on just one extra packet. If enabled use this instead of relying of fast retransmit. Suggested-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Leonard Crestez <redacted> --- Documentation/networking/ip-sysctl.rst | 5 +++++ include/net/netns/ipv4.h | 1 + net/ipv4/sysctl_net_ipv4.c | 7 +++++++ net/ipv4/tcp_ipv4.c | 1 + net/ipv4/tcp_output.c | 22 +++++++++++++++++++++- 5 files changed, 35 insertions(+), 1 deletion(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 108a5ee227d3..4f6ac69f61e7 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst@@ -325,10 +325,15 @@ tcp_mtu_probe_floor - INTEGER tcp_mtu_probe_autocork - BOOLEAN Take into account mtu probe size when accumulating data via autocorking. Default: 1 +tcp_mtu_probe_rack - BOOLEAN + Try to use shorter probes if RACK is also enabled + + Default: 1 + tcp_min_snd_mss - INTEGER TCP SYN and SYNACK messages usually advertise an ADVMSS option, as described in RFC 1122 and RFC 6691. If this ADVMSS option is smaller than tcp_min_snd_mss,
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index 3a2d8bf2b20a..298e65d8605c 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h@@ -113,10 +113,11 @@ struct netns_ipv4 { u8 sysctl_tcp_l3mdev_accept; #endif u8 sysctl_tcp_mtu_probing; int sysctl_tcp_mtu_probe_floor; int sysctl_tcp_mtu_probe_autocork; + int sysctl_tcp_mtu_probe_rack; int sysctl_tcp_base_mss; int sysctl_tcp_min_snd_mss; int sysctl_tcp_probe_threshold; u32 sysctl_tcp_probe_interval;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index e19176c17973..f9366f35ff9c 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c@@ -834,10 +834,17 @@ static struct ctl_table ipv4_net_table[] = { .data = &init_net.ipv4.sysctl_tcp_mtu_probe_autocork, .maxlen = sizeof(int), .mode = 0644, .proc_handler = proc_dointvec, }, + { + .procname = "tcp_mtu_probe_rack", + .data = &init_net.ipv4.sysctl_tcp_mtu_probe_rack, + .maxlen = sizeof(int), + .mode = 0644, + .proc_handler = proc_dointvec, + }, { .procname = "tcp_probe_threshold", .data = &init_net.ipv4.sysctl_tcp_probe_threshold, .maxlen = sizeof(int), .mode = 0644,
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 7e75423c08c9..4928fcd6e233 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c@@ -2890,10 +2890,11 @@ static int __net_init tcp_sk_init(struct net *net) net->ipv4.sysctl_tcp_min_snd_mss = TCP_MIN_SND_MSS; net->ipv4.sysctl_tcp_probe_threshold = TCP_PROBE_THRESHOLD; net->ipv4.sysctl_tcp_probe_interval = TCP_PROBE_INTERVAL; net->ipv4.sysctl_tcp_mtu_probe_floor = TCP_MIN_SND_MSS; net->ipv4.sysctl_tcp_mtu_probe_autocork = 1; + net->ipv4.sysctl_tcp_mtu_probe_rack = 1; net->ipv4.sysctl_tcp_keepalive_time = TCP_KEEPALIVE_TIME; net->ipv4.sysctl_tcp_keepalive_probes = TCP_KEEPALIVE_PROBES; net->ipv4.sysctl_tcp_keepalive_intvl = TCP_KEEPALIVE_INTVL;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 5a320d792ec4..7cd1e8fd9749 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c@@ -2311,27 +2311,47 @@ static bool tcp_can_coalesce_send_queue_head(struct sock *sk, int len) } return true; } +static int tcp_mtu_probe_is_rack(const struct sock *sk) +{ + struct net *net = sock_net(sk); + + return (net->ipv4.sysctl_tcp_recovery & TCP_RACK_LOSS_DETECTION && + net->ipv4.sysctl_tcp_mtu_probe_rack); +} + /* Calculate the size of an MTU probe * Probing the MTU requires one packets which is larger that current MSS as well * as enough following mtu-sized packets to ensure that a probe loss can be * detected without a full Retransmit Time out. */ int tcp_mtu_probe_size_needed(struct sock *sk, int *probe_size) { struct inet_connection_sock *icsk = inet_csk(sk); struct tcp_sock *tp = tcp_sk(sk); + struct net *net = sock_net(sk); int probe_size_val; int size_needed; /* This might be a little slow: */ probe_size_val = tcp_mtu_to_mss(sk, (icsk->icsk_mtup.search_high + icsk->icsk_mtup.search_low) >> 1); if (probe_size) *probe_size = probe_size_val; - size_needed = probe_size_val + (tp->reordering + 1) * tp->mss_cache; + + if (tcp_mtu_probe_is_rack(sk)) { + /* RACK allows recovering in min_rtt / 4 based on just one extra packet + * Use two to account for unrelated losses + */ + size_needed = probe_size_val + 2 * tp->mss_cache; + } else { + /* Without RACK send enough extra packets to trigger fast retransmit + * This is dynamic DupThresh + 1 + */ + size_needed = probe_size_val + (tp->reordering + 1) * tp->mss_cache; + } return size_needed; } /* Create a new MTU probe if we are ready.
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