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