[PATCH v3 net-next 4/6] tcp: add TCPAckCompressed SNMP counter

[Eric Dumazet <edumazet@google.com>]

This counter tracks number of ACK packets that the host has not sent,
thanks to ACK compression.

Sample output :

$ nstat -n;sleep 1;nstat|egrep "IpInReceives|IpOutRequests|TcpInSegs|TcpOutSegs|TcpExtTCPAckCompressed"
IpInReceives                    123250             0.0
IpOutRequests                   3684               0.0
TcpInSegs                       123251             0.0
TcpOutSegs                      3684               0.0
TcpExtTCPAckCompressed          119252             0.0

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
---
 include/uapi/linux/snmp.h | 1 +
 net/ipv4/proc.c           | 1 +
 net/ipv4/tcp_output.c     | 2 ++
 3 files changed, 4 insertions(+)

diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
index d02e859301ff499dd72a1c0e1b56bed10a9397a6..750d89120335eb489f698191edb6c5110969fa8c 100644
--- a/include/uapi/linux/snmp.h
+++ b/include/uapi/linux/snmp.h
@@ -278,6 +278,7 @@ enum
 	LINUX_MIB_TCPMTUPSUCCESS,		/* TCPMTUPSuccess */
 	LINUX_MIB_TCPDELIVERED,			/* TCPDelivered */
 	LINUX_MIB_TCPDELIVEREDCE,		/* TCPDeliveredCE */
+	LINUX_MIB_TCPACKCOMPRESSED,		/* TCPAckCompressed */
 	__LINUX_MIB_MAX
 };
 
diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
index 261b71d0ccc5c17c6032bf67eb8f842006766e64..6c1ff89a60fa0a3485dcc71fafc799e798d5dc11 100644
--- a/net/ipv4/proc.c
+++ b/net/ipv4/proc.c
@@ -298,6 +298,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPMTUPSuccess", LINUX_MIB_TCPMTUPSUCCESS),
 	SNMP_MIB_ITEM("TCPDelivered", LINUX_MIB_TCPDELIVERED),
 	SNMP_MIB_ITEM("TCPDeliveredCE", LINUX_MIB_TCPDELIVEREDCE),
+	SNMP_MIB_ITEM("TCPAckCompressed", LINUX_MIB_TCPACKCOMPRESSED),
 	SNMP_MIB_SENTINEL
 };
 
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 7ee98aad82b758674ca7f3e90bd3fc165e8fcd45..437bb7ceba7fd388abac1c12f2920b02be77bad9 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -165,6 +165,8 @@ static inline void tcp_event_ack_sent(struct sock *sk, unsigned int pkts)
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	if (unlikely(tp->compressed_ack)) {
+		NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPACKCOMPRESSED,
+			      tp->compressed_ack);
 		tp->compressed_ack = 0;
 		if (hrtimer_try_to_cancel(&tp->compressed_ack_timer) == 1)
 			__sock_put(sk);
-- 
2.17.0.441.gb46fe60e1d-goog