tcp: add SNMP counter for no. of duplicate segments reported by DSACK

There are two existing SNMP counters, TCPDSACKRecv and TCPDSACKOfoRecv, which are incremented depending on whether the DSACKed range is below the cumulative ACK sequence number or not. Unfortunately, these both implicitly assume each DSACK covers only one segment. This makes these counters unusable for estimating spurious retransmit rates, or real/non-spurious loss rate. This patch introduces a new SNMP counter, TCPDSACKRecvSegs, which tracks the estimated number of duplicate segments based on: (DSACKed sequence range) / MSS. This counter is usable for estimating spurious retransmit rates, or real/non-spurious loss rate. Signed-off-by: Priyaranjan Jha <[email protected]> Signed-off-by: Neal Cardwell <[email protected]> Signed-off-by: Yuchung Cheng <[email protected]> Signed-off-by: Soheil Hassas Yeganeh <[email protected]> Signed-off-by: David S. Miller <[email protected]>
bignaux · Jul 17, 2020 · e3a5a1e · e3a5a1e
1 parent a71d77e
commit e3a5a1e
Show file tree

Hide file tree

Showing 3 changed files with 3 additions and 0 deletions.
diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h
@@ -287,6 +287,7 @@ enum
 	LINUX_MIB_TCPFASTOPENPASSIVEALTKEY,	/* TCPFastOpenPassiveAltKey */
 	LINUX_MIB_TCPTIMEOUTREHASH,		/* TCPTimeoutRehash */
 	LINUX_MIB_TCPDUPLICATEDATAREHASH,	/* TCPDuplicateDataRehash */
+	LINUX_MIB_TCPDSACKRECVSEGS,		/* TCPDSACKRecvSegs */
 	__LINUX_MIB_MAX
 };
 

diff --git a/net/ipv4/proc.c b/net/ipv4/proc.c
@@ -292,6 +292,7 @@ static const struct snmp_mib snmp4_net_list[] = {
 	SNMP_MIB_ITEM("TCPFastOpenPassiveAltKey", LINUX_MIB_TCPFASTOPENPASSIVEALTKEY),
 	SNMP_MIB_ITEM("TcpTimeoutRehash", LINUX_MIB_TCPTIMEOUTREHASH),
 	SNMP_MIB_ITEM("TcpDuplicateDataRehash", LINUX_MIB_TCPDUPLICATEDATAREHASH),
+	SNMP_MIB_ITEM("TCPDSACKRecvSegs", LINUX_MIB_TCPDSACKRECVSEGS),
 	SNMP_MIB_SENTINEL
 };
 

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
@@ -1153,6 +1153,7 @@ static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb,
 	}
 
 	dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state);
+	NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECVSEGS, dup_segs);
 
 	/* D-SACK for already forgotten data... Do dumb counting. */
 	if (tp->undo_marker && tp->undo_retrans > 0 &&