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Date: Tue, 11 May 2021 15:04:17 +0300
From: Leonard Crestez <cdleonard@...il.com>
To: Neal Cardwell <ncardwell@...gle.com>,
Matt Mathis <mattmathis@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Willem de Bruijn <willemb@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
David Ahern <dsahern@...nel.org>,
John Heffner <johnwheffner@...il.com>,
Leonard Crestez <lcrestez@...venets.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Roopa Prabhu <roopa@...ulusnetworks.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC 2/3] tcp: Use mtu probes if RACK is enabled
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@...gle.com>
Signed-off-by: Leonard Crestez <cdleonard@...il.com>
---
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.
--
2.25.1
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