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add min_rtt time before retransmitting a packet when receiving a NAC… #9

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add min_rtt time before retransmitting a packet when receiving a NAC… #9

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31 changes: 30 additions & 1 deletion net/ipv4/tcp_input.c
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Original file line number Diff line number Diff line change
Expand Up @@ -3062,6 +3062,30 @@ static inline bool tcp_skb_should_handle_trimmed(const struct sock *sk,
return TCP_SKB_CB(skb)->trimmed && tcp_sk(sk)->rx_opt.trimming_ok;
}

/* Return true if a trimming NACK gives enough evidence to mark @skb lost.
*
* A duplicate NACK can arrive while the retransmission triggered by an earlier
* NACK is still in flight. In that case, avoid treating the retransmission as
* lost until at least one min RTT has elapsed since it was sent.
*/
static bool tcp_trimming_should_mark_lost(struct sock *sk, const struct sk_buff *skb)
{
struct tcp_sock *tp = tcp_sk(sk);
u8 sacked = TCP_SKB_CB(skb)->sacked;

if (sacked & TCPCB_SACKED_RETRANS) {
u32 rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp,
tcp_skb_timestamp_us(skb));

if (rtt_us < tcp_min_rtt(tp))
return false;
} else if (sacked & TCPCB_LOST) {
return false;
}

return true;
}

/* Locate the segment named by the NACK in the rtx queue and mark
* exactly one wire-MSS lost, so the recovery machinery retransmits
* only what the receiver said was missing — not the whole TSO
Expand All @@ -3084,7 +3108,8 @@ static inline bool tcp_skb_should_handle_trimmed(const struct sock *sk,
static void tcp_trimming_mark_lost(struct sock *sk)
{
struct sk_buff *skb = tcp_rtx_queue_head(sk);
u32 nack_seq = tcp_sk(sk)->rx_opt.nack_seq;
struct tcp_sock *tp = tcp_sk(sk);
u32 nack_seq = tp->rx_opt.nack_seq;

if (!skb)
return;
Expand All @@ -3099,6 +3124,8 @@ static void tcp_trimming_mark_lost(struct sock *sk)

/* Single wire segment already: mark the whole skb. */
if (tcp_skb_pcount(skb) <= 1) {
if (!tcp_trimming_should_mark_lost(sk, skb))
return;
tcp_mark_skb_lost(sk, skb);
return;
}
Expand Down Expand Up @@ -3139,6 +3166,8 @@ static void tcp_trimming_mark_lost(struct sock *sk)
tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, target,
mss, mss, GFP_ATOMIC);

if (!tcp_trimming_should_mark_lost(sk, target))
return;
tcp_mark_skb_lost(sk, target);
return;
}
Expand Down