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 <[email protected]>
---
v3: Updated doc as suggested by Neal Cardwell.
Updated variable location in struct netns_ipv4 as suggested by Kuniyuki
Iwashima.
v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
and Kuniyuki Iwashima.
---
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 f7dfde3b09a9..e7ec9026e5db 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1183,6 +1183,19 @@ 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 d6d9d1c1985a..086d1193c9ef 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -328,11 +328,10 @@ 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)
@@ -342,7 +341,16 @@ 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(const struct sock *sk)
diff --git a/include/net/netns/ipv4.h b/include/net/netns/ipv4.h
index d96d05b08819..73f43f699199 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -133,6 +133,8 @@ struct netns_ipv4 {
u8 sysctl_tcp_migrate_req;
u8 sysctl_tcp_comp_sack_nr;
u8 sysctl_tcp_backlog_ack_defer;
+ 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 e7f024d93572..f63a545a7374 100644
--- a/net/ipv4/sysctl_net_ipv4.c
+++ b/net/ipv4/sysctl_net_ipv4.c
@@ -1498,6 +1498,14 @@ 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 a441740616d7..f603ad9307af 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -3288,6 +3288,8 @@ 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 f207712eece1..7d0fe76d56ef 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. */
--
2.25.1
On Wed, Oct 11, 2023 at 01:30:44PM -0700, Haiyang Zhang wrote:
> 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 <[email protected]>
> ---
> v3: Updated doc as suggested by Neal Cardwell.
> Updated variable location in struct netns_ipv4 as suggested by Kuniyuki
> Iwashima.
>
> v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
> and Kuniyuki Iwashima.
Thanks,
this looks clean to me. It seems to address the review of v2.
And keeps the knob as syctl as discussed in v2.
Reviewed-by: Simon Horman <[email protected]>
On Wed, Oct 11, 2023 at 10:31 PM Haiyang Zhang <[email protected]> wrote:
>
> 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.
>
...
>
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index f207712eece1..7d0fe76d56ef 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. */
OK, but I do not think we solved the fundamental problem of using
jiffies for this heuristic,
especially for HZ=100 or HZ=250 builds.
Reviewed-by: Eric Dumazet <[email protected]>
On Wed, Oct 11, 2023 at 4:31 PM Haiyang Zhang <[email protected]> wrote:
>
> 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 <[email protected]>
> ---
> v3: Updated doc as suggested by Neal Cardwell.
> Updated variable location in struct netns_ipv4 as suggested by Kuniyuki
> Iwashima.
>
> v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
> and Kuniyuki Iwashima.
> ---
> 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(-)
Acked-by: Neal Cardwell <[email protected]>
Thanks!
neal
From: Haiyang Zhang <[email protected]>
Date: Wed, 11 Oct 2023 13:30:44 -0700
> 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 <[email protected]>
Reviewed-by: Kuniyuki Iwashima <[email protected]>
Thanks!
Hello:
This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <[email protected]>:
On Wed, 11 Oct 2023 13:30:44 -0700 you wrote:
> 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"")
>
> [...]
Here is the summary with links:
- [net-next,v3] tcp: Set pingpong threshold via sysctl
https://git.kernel.org/netdev/net-next/c/562b1fdf061b
You are awesome, thank you!
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