tcp: add SNMP counter for no. of duplicate segments reported by DSACK (e3a5a1e8) · Commits · 戴 / test

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 <priyarjha@google.com> Signed-off-by:

Neal Cardwell <ncardwell@google.com> Signed-off-by:

Yuchung Cheng <ycheng@google.com> Signed-off-by:

Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

include/uapi/linux/snmp.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -287,6 +287,7 @@ enum
		LINUX_MIB_TCPFASTOPENPASSIVEALTKEY, /* TCPFastOpenPassiveAltKey */
		LINUX_MIB_TCPTIMEOUTREHASH, /* TCPTimeoutRehash */
		LINUX_MIB_TCPDUPLICATEDATAREHASH, /* TCPDuplicateDataRehash */
		LINUX_MIB_TCPDSACKRECVSEGS, /* TCPDSACKRecvSegs */
		__LINUX_MIB_MAX
		};

net/ipv4/proc.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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
		};

net/ipv4/tcp_input.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -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 &&

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