[PATCH][mantic linux-azure] tcp: Set pingpong threshold via sysctl
Tim Gardner
tim.gardner at canonical.com
Tue Oct 24 17:32:37 UTC 2023
From: Haiyang Zhang <haiyangz at microsoft.com>
BugLink: https://bugs.launchpad.net/bugs/2040300
TCP pingpong threshold is 1 by default. But some applications, like SQL DB
may prefer a higher pingpong threshold to activate delayed acks in quick
ack mode for better performance.
The pingpong threshold and related code were changed to 3 in the year
2019 in:
commit 4a41f453bedf ("tcp: change pingpong threshold to 3")
And reverted to 1 in the year 2022 in:
commit 4d8f24eeedc5 ("Revert "tcp: change pingpong threshold to 3"")
There is no single value that fits all applications.
Add net.ipv4.tcp_pingpong_thresh sysctl tunable, so it can be tuned for
optimal performance based on the application needs.
Signed-off-by: Haiyang Zhang <haiyangz at microsoft.com>
Reviewed-by: Simon Horman <horms at kernel.org>
Reviewed-by: Eric Dumazet <edumazet at google.com>
Acked-by: Neal Cardwell <ncardwell at google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu at amazon.com>
Link: https://lore.kernel.org/r/1697056244-21888-1-git-send-email-haiyangz@microsoft.com
Signed-off-by: Jakub Kicinski <kuba at kernel.org>
(backported from commit 562b1fdf061bff9394ccd884456ed1173c224fdc linux-next)
[rtg - context adjustment]
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
Documentation/networking/ip-sysctl.rst | 13 +++++++++++++
include/net/inet_connection_sock.h | 16 ++++++++++++----
include/net/netns/ipv4.h | 2 ++
net/ipv4/sysctl_net_ipv4.c | 8 ++++++++
net/ipv4/tcp_ipv4.c | 2 ++
net/ipv4/tcp_output.c | 4 ++--
6 files changed, 39 insertions(+), 6 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 4a010a7cde7f..96dcb215cb0a 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1175,6 +1175,19 @@ tcp_plb_cong_thresh - INTEGER
Default: 128
+tcp_pingpong_thresh - INTEGER
+ The number of estimated data replies sent for estimated incoming data
+ requests that must happen before TCP considers that a connection is a
+ "ping-pong" (request-response) connection for which delayed
+ acknowledgments can provide benefits.
+
+ This threshold is 1 by default, but some applications may need a higher
+ threshold for optimal performance.
+
+ Possible Values: 1 - 255
+
+ Default: 1
+
UDP variables
=============
diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index c2b15f7e5516..b3e7eeb4cdfa 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -324,11 +324,10 @@ void inet_csk_update_fastreuse(struct inet_bind_bucket *tb,
struct dst_entry *inet_csk_update_pmtu(struct sock *sk, u32 mtu);
-#define TCP_PINGPONG_THRESH 1
-
static inline void inet_csk_enter_pingpong_mode(struct sock *sk)
{
- inet_csk(sk)->icsk_ack.pingpong = TCP_PINGPONG_THRESH;
+ inet_csk(sk)->icsk_ack.pingpong =
+ READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pingpong_thresh);
}
static inline void inet_csk_exit_pingpong_mode(struct sock *sk)
@@ -338,7 +337,16 @@ static inline void inet_csk_exit_pingpong_mode(struct sock *sk)
static inline bool inet_csk_in_pingpong_mode(struct sock *sk)
{
- return inet_csk(sk)->icsk_ack.pingpong >= TCP_PINGPONG_THRESH;
+ return inet_csk(sk)->icsk_ack.pingpong >=
+ READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_pingpong_thresh);
+}
+
+static inline void inet_csk_inc_pingpong_cnt(struct sock *sk)
+{
+ struct inet_connection_sock *icsk = inet_csk(sk);
+
+ if (icsk->icsk_ack.pingpong < U8_MAX)
+ icsk->icsk_ack.pingpong++;
}
static inline bool inet_csk_has_ulp(struct sock *sk)
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index f00374718159..5abe6eb15764 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -132,6 +132,8 @@ struct netns_ipv4 {
u8 sysctl_tcp_syncookies;
u8 sysctl_tcp_migrate_req;
u8 sysctl_tcp_comp_sack_nr;
+ u8 sysctl_tcp_pingpong_thresh;
+
int sysctl_tcp_reordering;
u8 sysctl_tcp_retries1;
u8 sysctl_tcp_retries2;
diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
index 2afb0870648b..77e8ff6cc0ac 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -1489,6 +1489,14 @@ static struct ctl_table ipv4_net_table[] = {
.extra1 = SYSCTL_ZERO,
.extra2 = SYSCTL_ONE,
},
+ {
+ .procname = "tcp_pingpong_thresh",
+ .data = &init_net.ipv4.sysctl_tcp_pingpong_thresh,
+ .maxlen = sizeof(u8),
+ .mode = 0644,
+ .proc_handler = proc_dou8vec_minmax,
+ .extra1 = SYSCTL_ONE,
+ },
{ }
};
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 2dbdc26da86e..aefe29ac3fec 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -3284,6 +3284,8 @@ static int __net_init tcp_sk_init(struct net *net)
net->ipv4.sysctl_tcp_syn_linear_timeouts = 4;
net->ipv4.sysctl_tcp_shrink_window = 0;
+ net->ipv4.sysctl_tcp_pingpong_thresh = 1;
+
return 0;
}
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 51d8638d4b4c..17449d39dcc4 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -170,10 +170,10 @@ static void tcp_event_data_sent(struct tcp_sock *tp,
tp->lsndtime = now;
/* If it is a reply for ato after last received
- * packet, enter pingpong mode.
+ * packet, increase pingpong count.
*/
if ((u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
- inet_csk_enter_pingpong_mode(sk);
+ inet_csk_inc_pingpong_cnt(sk);
}
/* Account for an ACK we sent. */
--
2.34.1
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