Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
2 : #include <linux/tcp.h>
3 : #include <net/tcp.h>
4 :
5 0 : static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2)
6 : {
7 0 : return t1 > t2 || (t1 == t2 && after(seq1, seq2));
8 : }
9 :
10 0 : static u32 tcp_rack_reo_wnd(const struct sock *sk)
11 : {
12 0 : struct tcp_sock *tp = tcp_sk(sk);
13 :
14 0 : if (!tp->reord_seen) {
15 : /* If reordering has not been observed, be aggressive during
16 : * the recovery or starting the recovery by DUPACK threshold.
17 : */
18 0 : if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery)
19 : return 0;
20 :
21 0 : if (tp->sacked_out >= tp->reordering &&
22 0 : !(sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_NO_DUPTHRESH))
23 : return 0;
24 : }
25 :
26 : /* To be more reordering resilient, allow min_rtt/4 settling delay.
27 : * Use min_rtt instead of the smoothed RTT because reordering is
28 : * often a path property and less related to queuing or delayed ACKs.
29 : * Upon receiving DSACKs, linearly increase the window up to the
30 : * smoothed RTT.
31 : */
32 0 : return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps,
33 : tp->srtt_us >> 3);
34 : }
35 :
36 0 : s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd)
37 : {
38 0 : return tp->rack.rtt_us + reo_wnd -
39 0 : tcp_stamp_us_delta(tp->tcp_mstamp, tcp_skb_timestamp_us(skb));
40 : }
41 :
42 : /* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01):
43 : *
44 : * Marks a packet lost, if some packet sent later has been (s)acked.
45 : * The underlying idea is similar to the traditional dupthresh and FACK
46 : * but they look at different metrics:
47 : *
48 : * dupthresh: 3 OOO packets delivered (packet count)
49 : * FACK: sequence delta to highest sacked sequence (sequence space)
50 : * RACK: sent time delta to the latest delivered packet (time domain)
51 : *
52 : * The advantage of RACK is it applies to both original and retransmitted
53 : * packet and therefore is robust against tail losses. Another advantage
54 : * is being more resilient to reordering by simply allowing some
55 : * "settling delay", instead of tweaking the dupthresh.
56 : *
57 : * When tcp_rack_detect_loss() detects some packets are lost and we
58 : * are not already in the CA_Recovery state, either tcp_rack_reo_timeout()
59 : * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will
60 : * make us enter the CA_Recovery state.
61 : */
62 0 : static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
63 : {
64 0 : struct tcp_sock *tp = tcp_sk(sk);
65 0 : struct sk_buff *skb, *n;
66 0 : u32 reo_wnd;
67 :
68 0 : *reo_timeout = 0;
69 0 : reo_wnd = tcp_rack_reo_wnd(sk);
70 0 : list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue,
71 : tcp_tsorted_anchor) {
72 0 : struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
73 0 : s32 remaining;
74 :
75 : /* Skip ones marked lost but not yet retransmitted */
76 0 : if ((scb->sacked & TCPCB_LOST) &&
77 : !(scb->sacked & TCPCB_SACKED_RETRANS))
78 0 : continue;
79 :
80 0 : if (!tcp_rack_sent_after(tp->rack.mstamp,
81 : tcp_skb_timestamp_us(skb),
82 : tp->rack.end_seq, scb->end_seq))
83 : break;
84 :
85 : /* A packet is lost if it has not been s/acked beyond
86 : * the recent RTT plus the reordering window.
87 : */
88 0 : remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd);
89 0 : if (remaining <= 0) {
90 0 : tcp_mark_skb_lost(sk, skb);
91 0 : list_del_init(&skb->tcp_tsorted_anchor);
92 : } else {
93 : /* Record maximum wait time */
94 0 : *reo_timeout = max_t(u32, *reo_timeout, remaining);
95 : }
96 : }
97 0 : }
98 :
99 0 : bool tcp_rack_mark_lost(struct sock *sk)
100 : {
101 0 : struct tcp_sock *tp = tcp_sk(sk);
102 0 : u32 timeout;
103 :
104 0 : if (!tp->rack.advanced)
105 : return false;
106 :
107 : /* Reset the advanced flag to avoid unnecessary queue scanning */
108 0 : tp->rack.advanced = 0;
109 0 : tcp_rack_detect_loss(sk, &timeout);
110 0 : if (timeout) {
111 0 : timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN;
112 0 : inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT,
113 0 : timeout, inet_csk(sk)->icsk_rto);
114 : }
115 0 : return !!timeout;
116 : }
117 :
118 : /* Record the most recently (re)sent time among the (s)acked packets
119 : * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from
120 : * draft-cheng-tcpm-rack-00.txt
121 : */
122 0 : void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq,
123 : u64 xmit_time)
124 : {
125 0 : u32 rtt_us;
126 :
127 0 : rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time);
128 0 : if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) {
129 : /* If the sacked packet was retransmitted, it's ambiguous
130 : * whether the retransmission or the original (or the prior
131 : * retransmission) was sacked.
132 : *
133 : * If the original is lost, there is no ambiguity. Otherwise
134 : * we assume the original can be delayed up to aRTT + min_rtt.
135 : * the aRTT term is bounded by the fast recovery or timeout,
136 : * so it's at least one RTT (i.e., retransmission is at least
137 : * an RTT later).
138 : */
139 : return;
140 : }
141 0 : tp->rack.advanced = 1;
142 0 : tp->rack.rtt_us = rtt_us;
143 0 : if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp,
144 : end_seq, tp->rack.end_seq)) {
145 0 : tp->rack.mstamp = xmit_time;
146 0 : tp->rack.end_seq = end_seq;
147 : }
148 : }
149 :
150 : /* We have waited long enough to accommodate reordering. Mark the expired
151 : * packets lost and retransmit them.
152 : */
153 0 : void tcp_rack_reo_timeout(struct sock *sk)
154 : {
155 0 : struct tcp_sock *tp = tcp_sk(sk);
156 0 : u32 timeout, prior_inflight;
157 0 : u32 lost = tp->lost;
158 :
159 0 : prior_inflight = tcp_packets_in_flight(tp);
160 0 : tcp_rack_detect_loss(sk, &timeout);
161 0 : if (prior_inflight != tcp_packets_in_flight(tp)) {
162 0 : if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) {
163 0 : tcp_enter_recovery(sk, false);
164 0 : if (!inet_csk(sk)->icsk_ca_ops->cong_control)
165 0 : tcp_cwnd_reduction(sk, 1, tp->lost - lost, 0);
166 : }
167 0 : tcp_xmit_retransmit_queue(sk);
168 : }
169 0 : if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS)
170 0 : tcp_rearm_rto(sk);
171 0 : }
172 :
173 : /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries.
174 : *
175 : * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded
176 : * by srtt), since there is possibility that spurious retransmission was
177 : * due to reordering delay longer than reo_wnd.
178 : *
179 : * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16)
180 : * no. of successful recoveries (accounts for full DSACK-based loss
181 : * recovery undo). After that, reset it to default (min_rtt/4).
182 : *
183 : * At max, reo_wnd is incremented only once per rtt. So that the new
184 : * DSACK on which we are reacting, is due to the spurious retx (approx)
185 : * after the reo_wnd has been updated last time.
186 : *
187 : * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than
188 : * absolute value to account for change in rtt.
189 : */
190 351 : void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs)
191 : {
192 351 : struct tcp_sock *tp = tcp_sk(sk);
193 :
194 351 : if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND ||
195 351 : !rs->prior_delivered)
196 : return;
197 :
198 : /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */
199 351 : if (before(rs->prior_delivered, tp->rack.last_delivered))
200 0 : tp->rack.dsack_seen = 0;
201 :
202 : /* Adjust the reo_wnd if update is pending */
203 351 : if (tp->rack.dsack_seen) {
204 0 : tp->rack.reo_wnd_steps = min_t(u32, 0xFF,
205 : tp->rack.reo_wnd_steps + 1);
206 0 : tp->rack.dsack_seen = 0;
207 0 : tp->rack.last_delivered = tp->delivered;
208 0 : tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH;
209 351 : } else if (!tp->rack.reo_wnd_persist) {
210 351 : tp->rack.reo_wnd_steps = 1;
211 : }
212 : }
213 :
214 : /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits
215 : * the next unacked packet upon receiving
216 : * a) three or more DUPACKs to start the fast recovery
217 : * b) an ACK acknowledging new data during the fast recovery.
218 : */
219 0 : void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced)
220 : {
221 0 : const u8 state = inet_csk(sk)->icsk_ca_state;
222 0 : struct tcp_sock *tp = tcp_sk(sk);
223 :
224 0 : if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) ||
225 0 : (state == TCP_CA_Recovery && snd_una_advanced)) {
226 0 : struct sk_buff *skb = tcp_rtx_queue_head(sk);
227 0 : u32 mss;
228 :
229 0 : if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
230 : return;
231 :
232 0 : mss = tcp_skb_mss(skb);
233 0 : if (tcp_skb_pcount(skb) > 1 && skb->len > mss)
234 0 : tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
235 : mss, mss, GFP_ATOMIC);
236 :
237 0 : tcp_mark_skb_lost(sk, skb);
238 : }
239 : }
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