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-rw-r--r--net/ipv4/tcp_input.c29
1 files changed, 15 insertions, 14 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 923e0e568bfa..ad1482dd215e 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2476,15 +2476,14 @@ static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
return false;
}
-/* The cwnd reduction in CWR and Recovery use the PRR algorithm
- * https://datatracker.ietf.org/doc/draft-ietf-tcpm-proportional-rate-reduction/
+/* The cwnd reduction in CWR and Recovery uses the PRR algorithm in RFC 6937.
* It computes the number of packets to send (sndcnt) based on packets newly
* delivered:
* 1) If the packets in flight is larger than ssthresh, PRR spreads the
* cwnd reductions across a full RTT.
- * 2) If packets in flight is lower than ssthresh (such as due to excess
- * losses and/or application stalls), do not perform any further cwnd
- * reductions, but instead slow start up to ssthresh.
+ * 2) Otherwise PRR uses packet conservation to send as much as delivered.
+ * But when the retransmits are acked without further losses, PRR
+ * slow starts cwnd up to ssthresh to speed up the recovery.
*/
static void tcp_init_cwnd_reduction(struct sock *sk)
{
@@ -2501,7 +2500,7 @@ static void tcp_init_cwnd_reduction(struct sock *sk)
}
static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
- int fast_rexmit)
+ int fast_rexmit, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
int sndcnt = 0;
@@ -2510,16 +2509,18 @@ static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
(tp->packets_out - tp->sacked_out);
tp->prr_delivered += newly_acked_sacked;
- if (tcp_packets_in_flight(tp) > tp->snd_ssthresh) {
+ if (delta < 0) {
u64 dividend = (u64)tp->snd_ssthresh * tp->prr_delivered +
tp->prior_cwnd - 1;
sndcnt = div_u64(dividend, tp->prior_cwnd) - tp->prr_out;
- } else {
+ } else if ((flag & FLAG_RETRANS_DATA_ACKED) &&
+ !(flag & FLAG_LOST_RETRANS)) {
sndcnt = min_t(int, delta,
max_t(int, tp->prr_delivered - tp->prr_out,
newly_acked_sacked) + 1);
+ } else {
+ sndcnt = min(delta, newly_acked_sacked);
}
-
sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
}
@@ -2580,7 +2581,7 @@ static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
tcp_try_keep_open(sk);
} else {
- tcp_cwnd_reduction(sk, prior_unsacked, 0);
+ tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
}
}
@@ -2737,7 +2738,7 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
/* Undo during fast recovery after partial ACK. */
static bool tcp_try_undo_partial(struct sock *sk, const int acked,
- const int prior_unsacked)
+ const int prior_unsacked, int flag)
{
struct tcp_sock *tp = tcp_sk(sk);
@@ -2753,7 +2754,7 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked,
* mark more packets lost or retransmit more.
*/
if (tp->retrans_out) {
- tcp_cwnd_reduction(sk, prior_unsacked, 0);
+ tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
return true;
}
@@ -2840,7 +2841,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
if (tcp_is_reno(tp) && is_dupack)
tcp_add_reno_sack(sk);
} else {
- if (tcp_try_undo_partial(sk, acked, prior_unsacked))
+ if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
return;
/* Partial ACK arrived. Force fast retransmit. */
do_lost = tcp_is_reno(tp) ||
@@ -2891,7 +2892,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
if (do_lost)
tcp_update_scoreboard(sk, fast_rexmit);
- tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit);
+ tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
tcp_xmit_retransmit_queue(sk);
}