From a71d77e6be1e29ec809cc7c85d9594e7769406cd Mon Sep 17 00:00:00 2001 From: Priyaranjan Jha Date: Thu, 16 Jul 2020 12:12:34 -0700 Subject: [PATCH 1/2] tcp: fix segment accounting when DSACK range covers multiple segments Currently, while processing DSACK, we assume DSACK covers only one segment. This leads to significant underestimation of DSACKs with LRO/GRO. This patch fixes segment accounting with DSACK by estimating segment count from DSACK sequence range / MSS. Signed-off-by: Priyaranjan Jha Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: Eric Dumazet Signed-off-by: Yousuk Seung Signed-off-by: David S. Miller --- net/ipv4/tcp_input.c | 80 ++++++++++++++++++++++++-------------------- 1 file changed, 44 insertions(+), 36 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index b03ca68d4111..5d6bbcb1e570 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -871,12 +871,41 @@ __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst) return min_t(__u32, cwnd, tp->snd_cwnd_clamp); } +struct tcp_sacktag_state { + /* Timestamps for earliest and latest never-retransmitted segment + * that was SACKed. RTO needs the earliest RTT to stay conservative, + * but congestion control should still get an accurate delay signal. + */ + u64 first_sackt; + u64 last_sackt; + u32 reord; + u32 sack_delivered; + int flag; + unsigned int mss_now; + struct rate_sample *rate; +}; + /* Take a notice that peer is sending D-SACKs */ -static void tcp_dsack_seen(struct tcp_sock *tp) +static u32 tcp_dsack_seen(struct tcp_sock *tp, u32 start_seq, + u32 end_seq, struct tcp_sacktag_state *state) { + u32 seq_len, dup_segs = 1; + + if (before(start_seq, end_seq)) { + seq_len = end_seq - start_seq; + if (seq_len > tp->mss_cache) + dup_segs = DIV_ROUND_UP(seq_len, tp->mss_cache); + } + tp->rx_opt.sack_ok |= TCP_DSACK_SEEN; tp->rack.dsack_seen = 1; - tp->dsack_dups++; + tp->dsack_dups += dup_segs; + + state->flag |= FLAG_DSACKING_ACK; + /* A spurious retransmission is delivered */ + state->sack_delivered += dup_segs; + + return dup_segs; } /* It's reordering when higher sequence was delivered (i.e. sacked) before @@ -1103,53 +1132,37 @@ static bool tcp_is_sackblock_valid(struct tcp_sock *tp, bool is_dsack, static bool tcp_check_dsack(struct sock *sk, const struct sk_buff *ack_skb, struct tcp_sack_block_wire *sp, int num_sacks, - u32 prior_snd_una) + u32 prior_snd_una, struct tcp_sacktag_state *state) { struct tcp_sock *tp = tcp_sk(sk); u32 start_seq_0 = get_unaligned_be32(&sp[0].start_seq); u32 end_seq_0 = get_unaligned_be32(&sp[0].end_seq); - bool dup_sack = false; + u32 dup_segs; if (before(start_seq_0, TCP_SKB_CB(ack_skb)->ack_seq)) { - dup_sack = true; - tcp_dsack_seen(tp); NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKRECV); } else if (num_sacks > 1) { u32 end_seq_1 = get_unaligned_be32(&sp[1].end_seq); u32 start_seq_1 = get_unaligned_be32(&sp[1].start_seq); - if (!after(end_seq_0, end_seq_1) && - !before(start_seq_0, start_seq_1)) { - dup_sack = true; - tcp_dsack_seen(tp); - NET_INC_STATS(sock_net(sk), - LINUX_MIB_TCPDSACKOFORECV); - } + if (after(end_seq_0, end_seq_1) || before(start_seq_0, start_seq_1)) + return false; + NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDSACKOFORECV); + } else { + return false; } + dup_segs = tcp_dsack_seen(tp, start_seq_0, end_seq_0, state); + /* D-SACK for already forgotten data... Do dumb counting. */ - if (dup_sack && tp->undo_marker && tp->undo_retrans > 0 && + if (tp->undo_marker && tp->undo_retrans > 0 && !after(end_seq_0, prior_snd_una) && after(end_seq_0, tp->undo_marker)) - tp->undo_retrans--; + tp->undo_retrans = max_t(int, 0, tp->undo_retrans - dup_segs); - return dup_sack; + return true; } -struct tcp_sacktag_state { - u32 reord; - /* Timestamps for earliest and latest never-retransmitted segment - * that was SACKed. RTO needs the earliest RTT to stay conservative, - * but congestion control should still get an accurate delay signal. - */ - u64 first_sackt; - u64 last_sackt; - struct rate_sample *rate; - int flag; - unsigned int mss_now; - u32 sack_delivered; -}; - /* Check if skb is fully within the SACK block. In presence of GSO skbs, * the incoming SACK may not exactly match but we can find smaller MSS * aligned portion of it that matches. Therefore we might need to fragment @@ -1692,12 +1705,7 @@ tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb, tcp_highest_sack_reset(sk); found_dup_sack = tcp_check_dsack(sk, ack_skb, sp_wire, - num_sacks, prior_snd_una); - if (found_dup_sack) { - state->flag |= FLAG_DSACKING_ACK; - /* A spurious retransmission is delivered */ - state->sack_delivered++; - } + num_sacks, prior_snd_una, state); /* Eliminate too old ACKs, but take into * account more or less fresh ones, they can From e3a5a1e8b6548f5d37328e2d3571edc5c9e6d7c0 Mon Sep 17 00:00:00 2001 From: Priyaranjan Jha Date: Thu, 16 Jul 2020 12:12:35 -0700 Subject: [PATCH 2/2] 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 Signed-off-by: Neal Cardwell Signed-off-by: Yuchung Cheng Signed-off-by: Soheil Hassas Yeganeh Signed-off-by: David S. Miller --- include/uapi/linux/snmp.h | 1 + net/ipv4/proc.c | 1 + net/ipv4/tcp_input.c | 1 + 3 files changed, 3 insertions(+) diff --git a/include/uapi/linux/snmp.h b/include/uapi/linux/snmp.h index 7d91f4debc48..cee9f8e6fce3 100644 --- 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 index 75545a829a2b..1074df726ec0 100644 --- 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 index 5d6bbcb1e570..82906deb7874 100644 --- 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 &&