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

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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>
This commit is contained in:
Priyaranjan Jha 2020-07-16 12:12:35 -07:00 committed by David S. Miller
parent a71d77e6be
commit e3a5a1e8b6
3 changed files with 3 additions and 0 deletions
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1
include/uapi/linux/snmp.h
View file

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

1
net/ipv4/proc.c
View file

@ -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
};

1
net/ipv4/tcp_input.c
View file

@ -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 &&