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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@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: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yousuk Seung <ysseung@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Priyaranjan Jha 2020-07-16 12:12:34 -07:00 committed by David S. Miller
parent dcc82bb072
commit a71d77e6be
1 changed files with 44 additions and 36 deletions
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80
net/ipv4/tcp_input.c
View File

@ -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