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Message-Id: <20200716191235.1556723-2-priyarjha@google.com>
Date: Thu, 16 Jul 2020 12:12:34 -0700
From: Priyaranjan Jha <priyarjha@...gle.com>
To: David Miller <davem@...emloft.net>
Cc: netdev@...r.kernel.org, Priyaranjan Jha <priyarjha@...gle.com>,
Neal Cardwell <ncardwell@...gle.com>,
Yuchung Cheng <ycheng@...gle.com>,
Soheil Hassas Yeganeh <soheil@...gle.com>,
Eric Dumazet <edumazet@...gle.com>,
Yousuk Seung <ysseung@...gle.com>
Subject: [PATCH net-next 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 <priyarjha@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Yousuk Seung <ysseung@...gle.com>
---
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
--
2.27.0.389.gc38d7665816-goog
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