1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/tcp.h> 3 #include <net/tcp.h> 4 5 static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2) 6 { 7 return t1 > t2 || (t1 == t2 && after(seq1, seq2)); 8 } 9 10 static u32 tcp_rack_reo_wnd(const struct sock *sk) 11 { 12 struct tcp_sock *tp = tcp_sk(sk); 13 14 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 if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery) 19 return 0; 20 21 if (tp->sacked_out >= tp->reordering && 22 !(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 return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps, 33 tp->srtt_us >> 3); 34 } 35 36 s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd) 37 { 38 return tp->rack.rtt_us + reo_wnd - 39 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 static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout) 63 { 64 struct tcp_sock *tp = tcp_sk(sk); 65 struct sk_buff *skb, *n; 66 u32 reo_wnd; 67 68 *reo_timeout = 0; 69 reo_wnd = tcp_rack_reo_wnd(sk); 70 list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue, 71 tcp_tsorted_anchor) { 72 struct tcp_skb_cb *scb = TCP_SKB_CB(skb); 73 s32 remaining; 74 75 /* Skip ones marked lost but not yet retransmitted */ 76 if ((scb->sacked & TCPCB_LOST) && 77 !(scb->sacked & TCPCB_SACKED_RETRANS)) 78 continue; 79 80 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 remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd); 89 if (remaining <= 0) { 90 tcp_mark_skb_lost(sk, skb); 91 list_del_init(&skb->tcp_tsorted_anchor); 92 } else { 93 /* Record maximum wait time */ 94 *reo_timeout = max_t(u32, *reo_timeout, remaining); 95 } 96 } 97 } 98 99 bool tcp_rack_mark_lost(struct sock *sk) 100 { 101 struct tcp_sock *tp = tcp_sk(sk); 102 u32 timeout; 103 104 if (!tp->rack.advanced) 105 return false; 106 107 /* Reset the advanced flag to avoid unnecessary queue scanning */ 108 tp->rack.advanced = 0; 109 tcp_rack_detect_loss(sk, &timeout); 110 if (timeout) { 111 timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN; 112 inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, 113 timeout, inet_csk(sk)->icsk_rto); 114 } 115 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 void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, 123 u64 xmit_time) 124 { 125 u32 rtt_us; 126 127 rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time); 128 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 tp->rack.advanced = 1; 142 tp->rack.rtt_us = rtt_us; 143 if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp, 144 end_seq, tp->rack.end_seq)) { 145 tp->rack.mstamp = xmit_time; 146 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 void tcp_rack_reo_timeout(struct sock *sk) 154 { 155 struct tcp_sock *tp = tcp_sk(sk); 156 u32 timeout, prior_inflight; 157 u32 lost = tp->lost; 158 159 prior_inflight = tcp_packets_in_flight(tp); 160 tcp_rack_detect_loss(sk, &timeout); 161 if (prior_inflight != tcp_packets_in_flight(tp)) { 162 if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) { 163 tcp_enter_recovery(sk, false); 164 if (!inet_csk(sk)->icsk_ca_ops->cong_control) 165 tcp_cwnd_reduction(sk, 1, tp->lost - lost, 0); 166 } 167 tcp_xmit_retransmit_queue(sk); 168 } 169 if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) 170 tcp_rearm_rto(sk); 171 } 172 173 /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries. 174 * 175 * If a DSACK is received that seems like it may have been due to reordering 176 * triggering fast recovery, increment reo_wnd by min_rtt/4 (upper bounded 177 * by srtt), since there is possibility that spurious retransmission was 178 * due to reordering delay longer than reo_wnd. 179 * 180 * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16) 181 * no. of successful recoveries (accounts for full DSACK-based loss 182 * recovery undo). After that, reset it to default (min_rtt/4). 183 * 184 * At max, reo_wnd is incremented only once per rtt. So that the new 185 * DSACK on which we are reacting, is due to the spurious retx (approx) 186 * after the reo_wnd has been updated last time. 187 * 188 * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than 189 * absolute value to account for change in rtt. 190 */ 191 void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs) 192 { 193 struct tcp_sock *tp = tcp_sk(sk); 194 195 if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND || 196 !rs->prior_delivered) 197 return; 198 199 /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */ 200 if (before(rs->prior_delivered, tp->rack.last_delivered)) 201 tp->rack.dsack_seen = 0; 202 203 /* Adjust the reo_wnd if update is pending */ 204 if (tp->rack.dsack_seen) { 205 tp->rack.reo_wnd_steps = min_t(u32, 0xFF, 206 tp->rack.reo_wnd_steps + 1); 207 tp->rack.dsack_seen = 0; 208 tp->rack.last_delivered = tp->delivered; 209 tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH; 210 } else if (!tp->rack.reo_wnd_persist) { 211 tp->rack.reo_wnd_steps = 1; 212 } 213 } 214 215 /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits 216 * the next unacked packet upon receiving 217 * a) three or more DUPACKs to start the fast recovery 218 * b) an ACK acknowledging new data during the fast recovery. 219 */ 220 void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced) 221 { 222 const u8 state = inet_csk(sk)->icsk_ca_state; 223 struct tcp_sock *tp = tcp_sk(sk); 224 225 if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) || 226 (state == TCP_CA_Recovery && snd_una_advanced)) { 227 struct sk_buff *skb = tcp_rtx_queue_head(sk); 228 u32 mss; 229 230 if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) 231 return; 232 233 mss = tcp_skb_mss(skb); 234 if (tcp_skb_pcount(skb) > 1 && skb->len > mss) 235 tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, 236 mss, mss, GFP_ATOMIC); 237 238 tcp_mark_skb_lost(sk, skb); 239 } 240 } 241