Branch data Line data Source code
1 : : // SPDX-License-Identifier: GPL-2.0
2 : : #include <linux/tcp.h>
3 : : #include <net/tcp.h>
4 : :
5 : 0 : void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
6 : : {
7 : : struct tcp_sock *tp = tcp_sk(sk);
8 : :
9 : 0 : tcp_skb_mark_lost_uncond_verify(tp, skb);
10 [ # # ]: 0 : if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
11 : : /* Account for retransmits that are lost again */
12 : 0 : TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
13 : 0 : tp->retrans_out -= tcp_skb_pcount(skb);
14 : 0 : NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
15 : : tcp_skb_pcount(skb));
16 : : }
17 : 0 : }
18 : :
19 : : static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2)
20 : : {
21 [ # # # # : 0 : return t1 > t2 || (t1 == t2 && after(seq1, seq2));
# # # # #
# # # ]
22 : : }
23 : :
24 : 0 : static u32 tcp_rack_reo_wnd(const struct sock *sk)
25 : : {
26 : : struct tcp_sock *tp = tcp_sk(sk);
27 : :
28 [ # # ]: 0 : if (!tp->reord_seen) {
29 : : /* If reordering has not been observed, be aggressive during
30 : : * the recovery or starting the recovery by DUPACK threshold.
31 : : */
32 [ # # ]: 0 : if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery)
33 : : return 0;
34 : :
35 [ # # # # ]: 0 : if (tp->sacked_out >= tp->reordering &&
36 : 0 : !(sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_NO_DUPTHRESH))
37 : : return 0;
38 : : }
39 : :
40 : : /* To be more reordering resilient, allow min_rtt/4 settling delay.
41 : : * Use min_rtt instead of the smoothed RTT because reordering is
42 : : * often a path property and less related to queuing or delayed ACKs.
43 : : * Upon receiving DSACKs, linearly increase the window up to the
44 : : * smoothed RTT.
45 : : */
46 : 0 : return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps,
47 : : tp->srtt_us >> 3);
48 : : }
49 : :
50 : 0 : s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd)
51 : : {
52 : 0 : return tp->rack.rtt_us + reo_wnd -
53 : 0 : tcp_stamp_us_delta(tp->tcp_mstamp, tcp_skb_timestamp_us(skb));
54 : : }
55 : :
56 : : /* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01):
57 : : *
58 : : * Marks a packet lost, if some packet sent later has been (s)acked.
59 : : * The underlying idea is similar to the traditional dupthresh and FACK
60 : : * but they look at different metrics:
61 : : *
62 : : * dupthresh: 3 OOO packets delivered (packet count)
63 : : * FACK: sequence delta to highest sacked sequence (sequence space)
64 : : * RACK: sent time delta to the latest delivered packet (time domain)
65 : : *
66 : : * The advantage of RACK is it applies to both original and retransmitted
67 : : * packet and therefore is robust against tail losses. Another advantage
68 : : * is being more resilient to reordering by simply allowing some
69 : : * "settling delay", instead of tweaking the dupthresh.
70 : : *
71 : : * When tcp_rack_detect_loss() detects some packets are lost and we
72 : : * are not already in the CA_Recovery state, either tcp_rack_reo_timeout()
73 : : * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will
74 : : * make us enter the CA_Recovery state.
75 : : */
76 : 0 : static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
77 : : {
78 : : struct tcp_sock *tp = tcp_sk(sk);
79 : : struct sk_buff *skb, *n;
80 : : u32 reo_wnd;
81 : :
82 : 0 : *reo_timeout = 0;
83 : 0 : reo_wnd = tcp_rack_reo_wnd(sk);
84 [ # # ]: 0 : list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue,
85 : : tcp_tsorted_anchor) {
86 : : struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
87 : : s32 remaining;
88 : :
89 : : /* Skip ones marked lost but not yet retransmitted */
90 [ # # ]: 0 : if ((scb->sacked & TCPCB_LOST) &&
91 : : !(scb->sacked & TCPCB_SACKED_RETRANS))
92 : 0 : continue;
93 : :
94 [ # # ]: 0 : if (!tcp_rack_sent_after(tp->rack.mstamp,
95 : : tcp_skb_timestamp_us(skb),
96 : : tp->rack.end_seq, scb->end_seq))
97 : : break;
98 : :
99 : : /* A packet is lost if it has not been s/acked beyond
100 : : * the recent RTT plus the reordering window.
101 : : */
102 : 0 : remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd);
103 [ # # ]: 0 : if (remaining <= 0) {
104 : 0 : tcp_mark_skb_lost(sk, skb);
105 : : list_del_init(&skb->tcp_tsorted_anchor);
106 : : } else {
107 : : /* Record maximum wait time */
108 : 0 : *reo_timeout = max_t(u32, *reo_timeout, remaining);
109 : : }
110 : : }
111 : 0 : }
112 : :
113 : 0 : void tcp_rack_mark_lost(struct sock *sk)
114 : : {
115 : : struct tcp_sock *tp = tcp_sk(sk);
116 : : u32 timeout;
117 : :
118 [ # # ]: 0 : if (!tp->rack.advanced)
119 : 0 : return;
120 : :
121 : : /* Reset the advanced flag to avoid unnecessary queue scanning */
122 : 0 : tp->rack.advanced = 0;
123 : 0 : tcp_rack_detect_loss(sk, &timeout);
124 [ # # ]: 0 : if (timeout) {
125 : 0 : timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN;
126 : 0 : inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT,
127 : 0 : timeout, inet_csk(sk)->icsk_rto);
128 : : }
129 : : }
130 : :
131 : : /* Record the most recently (re)sent time among the (s)acked packets
132 : : * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from
133 : : * draft-cheng-tcpm-rack-00.txt
134 : : */
135 : 0 : void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq,
136 : : u64 xmit_time)
137 : : {
138 : : u32 rtt_us;
139 : :
140 : 0 : rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time);
141 [ # # # # ]: 0 : if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) {
142 : : /* If the sacked packet was retransmitted, it's ambiguous
143 : : * whether the retransmission or the original (or the prior
144 : : * retransmission) was sacked.
145 : : *
146 : : * If the original is lost, there is no ambiguity. Otherwise
147 : : * we assume the original can be delayed up to aRTT + min_rtt.
148 : : * the aRTT term is bounded by the fast recovery or timeout,
149 : : * so it's at least one RTT (i.e., retransmission is at least
150 : : * an RTT later).
151 : : */
152 : 0 : return;
153 : : }
154 : 0 : tp->rack.advanced = 1;
155 : 0 : tp->rack.rtt_us = rtt_us;
156 [ # # ]: 0 : if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp,
157 : : end_seq, tp->rack.end_seq)) {
158 : 0 : tp->rack.mstamp = xmit_time;
159 : 0 : tp->rack.end_seq = end_seq;
160 : : }
161 : : }
162 : :
163 : : /* We have waited long enough to accommodate reordering. Mark the expired
164 : : * packets lost and retransmit them.
165 : : */
166 : 0 : void tcp_rack_reo_timeout(struct sock *sk)
167 : : {
168 : : struct tcp_sock *tp = tcp_sk(sk);
169 : : u32 timeout, prior_inflight;
170 : :
171 : : prior_inflight = tcp_packets_in_flight(tp);
172 : 0 : tcp_rack_detect_loss(sk, &timeout);
173 [ # # ]: 0 : if (prior_inflight != tcp_packets_in_flight(tp)) {
174 [ # # ]: 0 : if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) {
175 : 0 : tcp_enter_recovery(sk, false);
176 [ # # ]: 0 : if (!inet_csk(sk)->icsk_ca_ops->cong_control)
177 : 0 : tcp_cwnd_reduction(sk, 1, 0);
178 : : }
179 : 0 : tcp_xmit_retransmit_queue(sk);
180 : : }
181 [ # # ]: 0 : if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS)
182 : 0 : tcp_rearm_rto(sk);
183 : 0 : }
184 : :
185 : : /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries.
186 : : *
187 : : * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded
188 : : * by srtt), since there is possibility that spurious retransmission was
189 : : * due to reordering delay longer than reo_wnd.
190 : : *
191 : : * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16)
192 : : * no. of successful recoveries (accounts for full DSACK-based loss
193 : : * recovery undo). After that, reset it to default (min_rtt/4).
194 : : *
195 : : * At max, reo_wnd is incremented only once per rtt. So that the new
196 : : * DSACK on which we are reacting, is due to the spurious retx (approx)
197 : : * after the reo_wnd has been updated last time.
198 : : *
199 : : * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than
200 : : * absolute value to account for change in rtt.
201 : : */
202 : 0 : void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs)
203 : : {
204 : : struct tcp_sock *tp = tcp_sk(sk);
205 : :
206 [ # # # # ]: 0 : if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND ||
207 : 0 : !rs->prior_delivered)
208 : 0 : return;
209 : :
210 : : /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */
211 [ # # ]: 0 : if (before(rs->prior_delivered, tp->rack.last_delivered))
212 : 0 : tp->rack.dsack_seen = 0;
213 : :
214 : : /* Adjust the reo_wnd if update is pending */
215 [ # # ]: 0 : if (tp->rack.dsack_seen) {
216 : 0 : tp->rack.reo_wnd_steps = min_t(u32, 0xFF,
217 : : tp->rack.reo_wnd_steps + 1);
218 : 0 : tp->rack.dsack_seen = 0;
219 : 0 : tp->rack.last_delivered = tp->delivered;
220 : 0 : tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH;
221 [ # # ]: 0 : } else if (!tp->rack.reo_wnd_persist) {
222 : 0 : tp->rack.reo_wnd_steps = 1;
223 : : }
224 : : }
225 : :
226 : : /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits
227 : : * the next unacked packet upon receiving
228 : : * a) three or more DUPACKs to start the fast recovery
229 : : * b) an ACK acknowledging new data during the fast recovery.
230 : : */
231 : 0 : void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced)
232 : : {
233 : 0 : const u8 state = inet_csk(sk)->icsk_ca_state;
234 : : struct tcp_sock *tp = tcp_sk(sk);
235 : :
236 [ # # # # : 0 : if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) ||
# # ]
237 : 0 : (state == TCP_CA_Recovery && snd_una_advanced)) {
238 : : struct sk_buff *skb = tcp_rtx_queue_head(sk);
239 : : u32 mss;
240 : :
241 [ # # ]: 0 : if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST)
242 : 0 : return;
243 : :
244 : 0 : mss = tcp_skb_mss(skb);
245 [ # # # # ]: 0 : if (tcp_skb_pcount(skb) > 1 && skb->len > mss)
246 : 0 : tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb,
247 : : mss, mss, GFP_ATOMIC);
248 : :
249 : 0 : tcp_skb_mark_lost_uncond_verify(tp, skb);
250 : : }
251 : : }
|
