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tcp: Add PRR cwnd reduction for non-SACK loss

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This completes PRR cwnd reduction in all circumstances
for the base TCP stack (SACK loss recovery, ECN window reduction,
non-SACK loss recovery), preventing the arriving ACKs to
clock out new data at the old, too high rate. This
reduces the chance to induce additional losses while
recovering from loss (during congested network conditions).

For non-SACK loss recovery, each ACK is assumed to have
one MSS delivered. In order to prevent ACK-split attacks,
only one window worth of ACKs is considered to actually
have delivered new data.

MFC after: 6 weeks
Reviewed By: rrs, #transport
Sponsored by: NetApp, Inc.
Differential Revision: https://reviews.freebsd.org/D29441
This commit is contained in:
Richard Scheffenegger 2021-06-19 19:06:48 +02:00
parent 32f9c2ceb3
commit 74d7fc8753
1 changed files with 41 additions and 15 deletions
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42
sys/netinet/tcp_input.c
View File

@ -2612,8 +2612,7 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
cc_ack_received(tp, th, nsegs,
CC_DUPACK);
if (V_tcp_do_prr &&
IN_FASTRECOVERY(tp->t_flags) &&
(tp->t_flags & TF_SACK_PERMIT)) {
IN_FASTRECOVERY(tp->t_flags)) {
tcp_do_prr_ack(tp, th, &to);
} else if ((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK) &&
@ -2689,8 +2688,16 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
* snd_ssthresh is already updated by
* cc_cong_signal.
*/
if ((tp->t_flags & TF_SACK_PERMIT) &&
(to.to_flags & TOF_SACK)) {
tp->sackhint.prr_delivered =
tp->sackhint.sacked_bytes;
} else {
tp->sackhint.prr_delivered =
imin(tp->snd_max - tp->snd_una,
imin(INT_MAX / 65536,
tp->t_dupacks) * maxseg);
}
tp->sackhint.recover_fs = max(1,
tp->snd_nxt - tp->snd_una);
}
@ -3968,11 +3975,23 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
* (del_data) and an estimate of how many bytes are in the
* network.
*/
if (((tp->t_flags & TF_SACK_PERMIT) &&
(to->to_flags & TOF_SACK)) ||
(IN_CONGRECOVERY(tp->t_flags) &&
!IN_FASTRECOVERY(tp->t_flags))) {
del_data = tp->sackhint.delivered_data;
if (V_tcp_do_newsack)
pipe = tcp_compute_pipe(tp);
else
pipe = (tp->snd_nxt - tp->snd_fack) + tp->sackhint.sack_bytes_rexmit;
pipe = (tp->snd_nxt - tp->snd_fack) +
tp->sackhint.sack_bytes_rexmit;
} else {
if (tp->sackhint.prr_delivered < (tcprexmtthresh * maxseg +
tp->snd_recover - tp->snd_una))
del_data = maxseg;
pipe = imax(0, tp->snd_max - tp->snd_una -
imin(INT_MAX / 65536, tp->t_dupacks) * maxseg);
}
tp->sackhint.prr_delivered += del_data;
/*
* Proportional Rate Reduction
@ -3985,7 +4004,7 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
tp->snd_ssthresh, tp->sackhint.recover_fs) -
tp->sackhint.prr_out;
} else {
if (V_tcp_do_prr_conservative)
if (V_tcp_do_prr_conservative || (del_data == 0))
limit = tp->sackhint.prr_delivered -
tp->sackhint.prr_out;
else
@ -4001,11 +4020,18 @@ tcp_do_prr_ack(struct tcpcb *tp, struct tcphdr *th, struct tcpopt *to)
* accordingly.
*/
if (IN_FASTRECOVERY(tp->t_flags)) {
tp->snd_cwnd = imax(maxseg, tp->snd_nxt - tp->snd_recover +
tp->sackhint.sack_bytes_rexmit + (snd_cnt * maxseg));
if ((tp->t_flags & TF_SACK_PERMIT) &&
(to->to_flags & TOF_SACK)) {
tp->snd_cwnd = tp->snd_nxt - tp->snd_recover +
tp->sackhint.sack_bytes_rexmit +
(snd_cnt * maxseg);
} else {
tp->snd_cwnd = (tp->snd_max - tp->snd_una) +
(snd_cnt * maxseg);
}
} else if (IN_CONGRECOVERY(tp->t_flags))
tp->snd_cwnd = imax(maxseg, pipe - del_data +
(snd_cnt * maxseg));
tp->snd_cwnd = pipe - del_data + (snd_cnt * maxseg);
tp->snd_cwnd = imax(maxseg, tp->snd_cwnd);
}
/*