[PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Haiyang Zhang]

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@microsoft.com>
---
v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
and Kuniyuki Iwashima.

---
 Documentation/networking/ip-sysctl.rst |  8 ++++++++
 include/net/inet_connection_sock.h     | 16 ++++++++++++----
 include/net/netns/ipv4.h               |  1 +
 net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
 net/ipv4/tcp_ipv4.c                    |  2 ++
 net/ipv4/tcp_output.c                  |  4 ++--
 6 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index 5bfa1837968c..c0308b65dc2f 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER
 
 	Default: 128
 
+tcp_pingpong_thresh - INTEGER
+	TCP pingpong threshold is 1 by default, but some application 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 5d2fcc137b88..0182f27bce40 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -325,11 +325,10 @@ 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)
@@ -339,7 +338,16 @@ 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..9f1b3eb9473e 100644
--- a/include/net/netns/ipv4.h
+++ b/include/net/netns/ipv4.h
@@ -191,6 +191,7 @@ struct netns_ipv4 {
 	u8 sysctl_tcp_plb_rehash_rounds;
 	u8 sysctl_tcp_plb_suspend_rto_sec;
 	int sysctl_tcp_plb_cong_thresh;
+	u8 sysctl_tcp_pingpong_thresh;
 
 	int sysctl_udp_wmem_min;
 	int sysctl_udp_rmem_min;
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 8885552dff8e..5736a736b59c 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

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Neal Cardwell]

On Tue, Oct 10, 2023 at 3:24 PM Haiyang Zhang <haiyangz@microsoft.com> 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 <haiyangz@microsoft.com>
> ---
> v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
> and Kuniyuki Iwashima.
>
> ---
>  Documentation/networking/ip-sysctl.rst |  8 ++++++++
>  include/net/inet_connection_sock.h     | 16 ++++++++++++----
>  include/net/netns/ipv4.h               |  1 +
>  net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
>  net/ipv4/tcp_ipv4.c                    |  2 ++
>  net/ipv4/tcp_output.c                  |  4 ++--
>  6 files changed, 33 insertions(+), 6 deletions(-)
>
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 5bfa1837968c..c0308b65dc2f 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER
>
>         Default: 128
>
> +tcp_pingpong_thresh - INTEGER
> +       TCP pingpong threshold is 1 by default, but some application may need a
> +       higher threshold for optimal performance.
> +
> +       Possible Values: 1 - 255
> +
> +       Default: 1
> +

It would be good to document what the meaning of the parameter is.
Perhaps consider something like:

'The number of estimated data replies sent for estimated incoming data
requests that must happen before TCP estimates 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.'

Thanks for the patch!

best,
neal

RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Haiyang Zhang]

> -----Original Message-----
> From: Neal Cardwell <ncardwell@google.com>
> Sent: Tuesday, October 10, 2023 4:07 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: linux-hyperv@vger.kernel.org; netdev@vger.kernel.org; KY Srinivasan
> <kys@microsoft.com>; davem@davemloft.net; edumazet@google.com;
> kuba@kernel.org; pabeni@redhat.com; corbet@lwn.net;
> dsahern@kernel.org; ycheng@google.com; kuniyu@amazon.com;
> morleyd@google.com; mfreemon@cloudflare.com; mubashirq@google.com;
> linux-doc@vger.kernel.org; weiwan@google.com; linux-
> kernel@vger.kernel.org
> Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> 
> [You don't often get email from ncardwell@google.com. Learn why this is
> important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> On Tue, Oct 10, 2023 at 3:24 PM Haiyang Zhang <haiyangz@microsoft.com>
> 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 <haiyangz@microsoft.com>
> > ---
> > v2: Make it per-namesapce setting, and other updates suggested by Neal
> Cardwell,
> > and Kuniyuki Iwashima.
> >
> > ---
> >  Documentation/networking/ip-sysctl.rst |  8 ++++++++
> >  include/net/inet_connection_sock.h     | 16 ++++++++++++----
> >  include/net/netns/ipv4.h               |  1 +
> >  net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
> >  net/ipv4/tcp_ipv4.c                    |  2 ++
> >  net/ipv4/tcp_output.c                  |  4 ++--
> >  6 files changed, 33 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/networking/ip-sysctl.rst
> b/Documentation/networking/ip-sysctl.rst
> > index 5bfa1837968c..c0308b65dc2f 100644
> > --- a/Documentation/networking/ip-sysctl.rst
> > +++ b/Documentation/networking/ip-sysctl.rst
> > @@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER
> >
> >         Default: 128
> >
> > +tcp_pingpong_thresh - INTEGER
> > +       TCP pingpong threshold is 1 by default, but some application may need
> a
> > +       higher threshold for optimal performance.
> > +
> > +       Possible Values: 1 - 255
> > +
> > +       Default: 1
> > +
> 
> It would be good to document what the meaning of the parameter is.
> Perhaps consider something like:
> 
> 'The number of estimated data replies sent for estimated incoming data
> requests that must happen before TCP estimates 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.'
> 
Will do.

Thanks,
- Haiyang

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Kuniyuki Iwashima]

From: Haiyang Zhang <haiyangz@microsoft.com>
Date: Tue, 10 Oct 2023 12:23:30 -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 <haiyangz@microsoft.com>
> ---
> v2: Make it per-namesapce setting, and other updates suggested by Neal Cardwell,
> and Kuniyuki Iwashima.
> 
> ---
>  Documentation/networking/ip-sysctl.rst |  8 ++++++++
>  include/net/inet_connection_sock.h     | 16 ++++++++++++----
>  include/net/netns/ipv4.h               |  1 +
>  net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
>  net/ipv4/tcp_ipv4.c                    |  2 ++
>  net/ipv4/tcp_output.c                  |  4 ++--
>  6 files changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
> index 5bfa1837968c..c0308b65dc2f 100644
> --- a/Documentation/networking/ip-sysctl.rst
> +++ b/Documentation/networking/ip-sysctl.rst
> @@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER
>  
>  	Default: 128
>  
> +tcp_pingpong_thresh - INTEGER
> +	TCP pingpong threshold is 1 by default, but some application 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 5d2fcc137b88..0182f27bce40 100644
> --- a/include/net/inet_connection_sock.h
> +++ b/include/net/inet_connection_sock.h
> @@ -325,11 +325,10 @@ 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)
> @@ -339,7 +338,16 @@ 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..9f1b3eb9473e 100644
> --- a/include/net/netns/ipv4.h
> +++ b/include/net/netns/ipv4.h
> @@ -191,6 +191,7 @@ struct netns_ipv4 {
>  	u8 sysctl_tcp_plb_rehash_rounds;
>  	u8 sysctl_tcp_plb_suspend_rto_sec;
>  	int sysctl_tcp_plb_cong_thresh;
> +	u8 sysctl_tcp_pingpong_thresh;
>  
>  	int sysctl_udp_wmem_min;
>  	int sysctl_udp_rmem_min;

Maybe a hole after sysctl_tcp_backlog_ack_defer is a good place
to put a new TCP knob.

After sysctl_tcp_plb_cong_thresh, we can fill 1-byte hole but the
cacheline seems cold for TCP.

$ pahole -C netns_ipv4 vmlinux
struct netns_ipv4 {
...
	u8                         sysctl_tcp_backlog_ack_defer; /*   402     1 */

	/* XXX 1 byte hole, try to pack */

	int                        sysctl_tcp_reordering; /*   404     4 */
...
	int                        sysctl_tcp_plb_cong_thresh; /*   572     4 */
	/* --- cacheline 9 boundary (576 bytes) --- */
	int                        sysctl_udp_wmem_min;  /*   576     4 */
	int                        sysctl_udp_rmem_min;  /*   580     4 */
	u8                         sysctl_fib_notify_on_flag_change; /*   584     1 */
	u8                         sysctl_tcp_syn_linear_timeouts; /*   585     1 */
	u8                         sysctl_igmp_llm_reports; /*   586     1 */

	/* XXX 1 byte hole, try to pack */
...


> 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 8885552dff8e..5736a736b59c 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

RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Haiyang Zhang]

> -----Original Message-----
> From: Kuniyuki Iwashima <kuniyu@amazon.com>
> Sent: Tuesday, October 10, 2023 4:12 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: corbet@lwn.net; davem@davemloft.net; dsahern@kernel.org;
> edumazet@google.com; kuba@kernel.org; kuniyu@amazon.com; KY
> Srinivasan <kys@microsoft.com>; linux-doc@vger.kernel.org; linux-
> hyperv@vger.kernel.org; linux-kernel@vger.kernel.org;
> mfreemon@cloudflare.com; morleyd@google.com; mubashirq@google.com;
> ncardwell@google.com; netdev@vger.kernel.org; pabeni@redhat.com;
> weiwan@google.com; ycheng@google.com
> Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> 
> [You don't often get email from kuniyu@amazon.com. Learn why this is
> important at https://aka.ms/LearnAboutSenderIdentification ]
> 
> From: Haiyang Zhang <haiyangz@microsoft.com>
> Date: Tue, 10 Oct 2023 12:23:30 -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 <haiyangz@microsoft.com>
> > ---
> > v2: Make it per-namesapce setting, and other updates suggested by Neal
> Cardwell,
> > and Kuniyuki Iwashima.
> >
> > ---
> >  Documentation/networking/ip-sysctl.rst |  8 ++++++++
> >  include/net/inet_connection_sock.h     | 16 ++++++++++++----
> >  include/net/netns/ipv4.h               |  1 +
> >  net/ipv4/sysctl_net_ipv4.c             |  8 ++++++++
> >  net/ipv4/tcp_ipv4.c                    |  2 ++
> >  net/ipv4/tcp_output.c                  |  4 ++--
> >  6 files changed, 33 insertions(+), 6 deletions(-)
> >
> > diff --git a/Documentation/networking/ip-sysctl.rst
> b/Documentation/networking/ip-sysctl.rst
> > index 5bfa1837968c..c0308b65dc2f 100644
> > --- a/Documentation/networking/ip-sysctl.rst
> > +++ b/Documentation/networking/ip-sysctl.rst
> > @@ -1183,6 +1183,14 @@ tcp_plb_cong_thresh - INTEGER
> >
> >       Default: 128
> >
> > +tcp_pingpong_thresh - INTEGER
> > +     TCP pingpong threshold is 1 by default, but some application 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 5d2fcc137b88..0182f27bce40 100644
> > --- a/include/net/inet_connection_sock.h
> > +++ b/include/net/inet_connection_sock.h
> > @@ -325,11 +325,10 @@ 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)
> > @@ -339,7 +338,16 @@ 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..9f1b3eb9473e 100644
> > --- a/include/net/netns/ipv4.h
> > +++ b/include/net/netns/ipv4.h
> > @@ -191,6 +191,7 @@ struct netns_ipv4 {
> >       u8 sysctl_tcp_plb_rehash_rounds;
> >       u8 sysctl_tcp_plb_suspend_rto_sec;
> >       int sysctl_tcp_plb_cong_thresh;
> > +     u8 sysctl_tcp_pingpong_thresh;
> >
> >       int sysctl_udp_wmem_min;
> >       int sysctl_udp_rmem_min;
> 
> Maybe a hole after sysctl_tcp_backlog_ack_defer is a good place
> to put a new TCP knob.
> 
> After sysctl_tcp_plb_cong_thresh, we can fill 1-byte hole but the
> cacheline seems cold for TCP.
> 
> $ pahole -C netns_ipv4 vmlinux
> struct netns_ipv4 {
> ...
>         u8                         sysctl_tcp_backlog_ack_defer; /*   402     1 */
> 
>         /* XXX 1 byte hole, try to pack */
> 
>         int                        sysctl_tcp_reordering; /*   404     4 */
> ...
>         int                        sysctl_tcp_plb_cong_thresh; /*   572     4 */
>         /* --- cacheline 9 boundary (576 bytes) --- */
>         int                        sysctl_udp_wmem_min;  /*   576     4 */
>         int                        sysctl_udp_rmem_min;  /*   580     4 */
>         u8                         sysctl_fib_notify_on_flag_change; /*   584     1 */
>         u8                         sysctl_tcp_syn_linear_timeouts; /*   585     1 */
>         u8                         sysctl_igmp_llm_reports; /*   586     1 */
> 
>         /* XXX 1 byte hole, try to pack */
> ...
> 

Will do.

Thanks,
- Haiyang

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Stephen Hemminger]

On Tue, 10 Oct 2023 12:23:30 -0700
Haiyang Zhang <haiyangz@microsoft.com> 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 <haiyangz@microsoft.com>

If this an application specific optimization, it should be in a socket option
rather than system wide via sysctl.

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Yuchung Cheng]

On Tue, Oct 10, 2023 at 3:14 PM Stephen Hemminger
<stephen@networkplumber.org> wrote:
>
> On Tue, 10 Oct 2023 12:23:30 -0700
> Haiyang Zhang <haiyangz@microsoft.com> 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 <haiyangz@microsoft.com>
>
> If this an application specific optimization, it should be in a socket option
> rather than system wide via sysctl.
Initially I had a similar comment but later decided a sysctl could
still be useful if
1) the entire host (e.g. virtual machine) is dedicated to that application
2) that application is difficult to change

RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Haiyang Zhang]

> -----Original Message-----
> From: Yuchung Cheng <ycheng@google.com>
> Sent: Tuesday, October 10, 2023 6:27 PM
> To: Stephen Hemminger <stephen@networkplumber.org>
> Cc: Haiyang Zhang <haiyangz@microsoft.com>; linux-hyperv@vger.kernel.org;
> netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com; corbet@lwn.net; dsahern@kernel.org;
> ncardwell@google.com; kuniyu@amazon.com; morleyd@google.com;
> mfreemon@cloudflare.com; mubashirq@google.com; linux-
> doc@vger.kernel.org; weiwan@google.com; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> 
> On Tue, Oct 10, 2023 at 3:14 PM Stephen Hemminger
> <stephen@networkplumber.org> wrote:
> >
> > On Tue, 10 Oct 2023 12:23:30 -0700
> > Haiyang Zhang <haiyangz@microsoft.com> 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 <haiyangz@microsoft.com>
> >
> > If this an application specific optimization, it should be in a socket option
> > rather than system wide via sysctl.
> Initially I had a similar comment but later decided a sysctl could
> still be useful if
> 1) the entire host (e.g. virtual machine) is dedicated to that application
> 2) that application is difficult to change

Yes, the customer actually wants a global setting. But as suggested by Neal,
I changed it to be per-namespace to match other TCP tunables.

Thanks,
- Haiyang

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Stephen Hemminger]

On Tue, 10 Oct 2023 22:59:49 +0000
Haiyang Zhang <haiyangz@microsoft.com> wrote:

> > > If this an application specific optimization, it should be in a socket option
> > > rather than system wide via sysctl.  
> > Initially I had a similar comment but later decided a sysctl could
> > still be useful if
> > 1) the entire host (e.g. virtual machine) is dedicated to that application
> > 2) that application is difficult to change  
> 
> Yes, the customer actually wants a global setting. But as suggested by Neal,
> I changed it to be per-namespace to match other TCP tunables.

Like congestion control choice, it could be both a sysctl and a socket option.
The reason is that delayed ack is already controlled by socket options.

RE: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Haiyang Zhang]

> -----Original Message-----
> From: Stephen Hemminger <stephen@networkplumber.org>
> Sent: Tuesday, October 10, 2023 10:16 PM
> To: Haiyang Zhang <haiyangz@microsoft.com>
> Cc: Yuchung Cheng <ycheng@google.com>; linux-hyperv@vger.kernel.org;
> netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> pabeni@redhat.com; corbet@lwn.net; dsahern@kernel.org;
> ncardwell@google.com; kuniyu@amazon.com; morleyd@google.com;
> mfreemon@cloudflare.com; mubashirq@google.com; linux-
> doc@vger.kernel.org; weiwan@google.com; linux-kernel@vger.kernel.org
> Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> 
> On Tue, 10 Oct 2023 22:59:49 +0000
> Haiyang Zhang <haiyangz@microsoft.com> wrote:
> 
> > > > If this an application specific optimization, it should be in a socket option
> > > > rather than system wide via sysctl.
> > > Initially I had a similar comment but later decided a sysctl could
> > > still be useful if
> > > 1) the entire host (e.g. virtual machine) is dedicated to that application
> > > 2) that application is difficult to change
> >
> > Yes, the customer actually wants a global setting. But as suggested by Neal,
> > I changed it to be per-namespace to match other TCP tunables.
> 
> Like congestion control choice, it could be both a sysctl and a socket option.
> The reason is that delayed ack is already controlled by socket options.

I see. I am updating the doc and variable location for this sysctl tunable patch 
as suggested by the reviewers, and will resubmit it.

I will also work on a separate patch for the setsockopt option.

Thanks,
- Haiyang

Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl

[Eric Dumazet]

On Wed, Oct 11, 2023 at 8:49 PM Haiyang Zhang <haiyangz@microsoft.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Stephen Hemminger <stephen@networkplumber.org>
> > Sent: Tuesday, October 10, 2023 10:16 PM
> > To: Haiyang Zhang <haiyangz@microsoft.com>
> > Cc: Yuchung Cheng <ycheng@google.com>; linux-hyperv@vger.kernel.org;
> > netdev@vger.kernel.org; KY Srinivasan <kys@microsoft.com>;
> > davem@davemloft.net; edumazet@google.com; kuba@kernel.org;
> > pabeni@redhat.com; corbet@lwn.net; dsahern@kernel.org;
> > ncardwell@google.com; kuniyu@amazon.com; morleyd@google.com;
> > mfreemon@cloudflare.com; mubashirq@google.com; linux-
> > doc@vger.kernel.org; weiwan@google.com; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH net-next,v2] tcp: Set pingpong threshold via sysctl
> >
> > On Tue, 10 Oct 2023 22:59:49 +0000
> > Haiyang Zhang <haiyangz@microsoft.com> wrote:
> >
> > > > > If this an application specific optimization, it should be in a socket option
> > > > > rather than system wide via sysctl.
> > > > Initially I had a similar comment but later decided a sysctl could
> > > > still be useful if
> > > > 1) the entire host (e.g. virtual machine) is dedicated to that application
> > > > 2) that application is difficult to change
> > >
> > > Yes, the customer actually wants a global setting. But as suggested by Neal,
> > > I changed it to be per-namespace to match other TCP tunables.
> >
> > Like congestion control choice, it could be both a sysctl and a socket option.
> > The reason is that delayed ack is already controlled by socket options.
>
> I see. I am updating the doc and variable location for this sysctl tunable patch
> as suggested by the reviewers, and will resubmit it.
>
> I will also work on a separate patch for the setsockopt option.
>
>

I am not sure about adding a socket option, and finding room in the
socket structure.

See our recent effort reshuffling fields in tcp socket for better
performance (stalled at this time).

I would rather experiment first with a sysctl.