From a71d77e6be1e29ec809cc7c85d9594e7769406cd Mon Sep 17 00:00:00 2001 From: Priyaranjan Jha Date: Thu, 16 Jul 2020 12:12:34 -0700 Subject: [PATCH] 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 -- 2.11.0