| // SPDX-License-Identifier: GPL-2.0 |
| #include <linux/tcp.h> |
| #include <net/tcp.h> |
| |
| static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2) |
| { |
| return t1 > t2 || (t1 == t2 && after(seq1, seq2)); |
| } |
| |
| static u32 tcp_rack_reo_wnd(const struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (!tp->reord_seen) { |
| /* If reordering has not been observed, be aggressive during |
| * the recovery or starting the recovery by DUPACK threshold. |
| */ |
| if (inet_csk(sk)->icsk_ca_state >= TCP_CA_Recovery) |
| return 0; |
| |
| if (tp->sacked_out >= tp->reordering && |
| !(sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_NO_DUPTHRESH)) |
| return 0; |
| } |
| |
| /* To be more reordering resilient, allow min_rtt/4 settling delay. |
| * Use min_rtt instead of the smoothed RTT because reordering is |
| * often a path property and less related to queuing or delayed ACKs. |
| * Upon receiving DSACKs, linearly increase the window up to the |
| * smoothed RTT. |
| */ |
| return min((tcp_min_rtt(tp) >> 2) * tp->rack.reo_wnd_steps, |
| tp->srtt_us >> 3); |
| } |
| |
| s32 tcp_rack_skb_timeout(struct tcp_sock *tp, struct sk_buff *skb, u32 reo_wnd) |
| { |
| return tp->rack.rtt_us + reo_wnd - |
| tcp_stamp_us_delta(tp->tcp_mstamp, tcp_skb_timestamp_us(skb)); |
| } |
| |
| /* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01): |
| * |
| * Marks a packet lost, if some packet sent later has been (s)acked. |
| * The underlying idea is similar to the traditional dupthresh and FACK |
| * but they look at different metrics: |
| * |
| * dupthresh: 3 OOO packets delivered (packet count) |
| * FACK: sequence delta to highest sacked sequence (sequence space) |
| * RACK: sent time delta to the latest delivered packet (time domain) |
| * |
| * The advantage of RACK is it applies to both original and retransmitted |
| * packet and therefore is robust against tail losses. Another advantage |
| * is being more resilient to reordering by simply allowing some |
| * "settling delay", instead of tweaking the dupthresh. |
| * |
| * When tcp_rack_detect_loss() detects some packets are lost and we |
| * are not already in the CA_Recovery state, either tcp_rack_reo_timeout() |
| * or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will |
| * make us enter the CA_Recovery state. |
| */ |
| static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| struct sk_buff *skb, *n; |
| u32 reo_wnd; |
| |
| *reo_timeout = 0; |
| reo_wnd = tcp_rack_reo_wnd(sk); |
| list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue, |
| tcp_tsorted_anchor) { |
| struct tcp_skb_cb *scb = TCP_SKB_CB(skb); |
| s32 remaining; |
| |
| /* Skip ones marked lost but not yet retransmitted */ |
| if ((scb->sacked & TCPCB_LOST) && |
| !(scb->sacked & TCPCB_SACKED_RETRANS)) |
| continue; |
| |
| if (!tcp_rack_sent_after(tp->rack.mstamp, |
| tcp_skb_timestamp_us(skb), |
| tp->rack.end_seq, scb->end_seq)) |
| break; |
| |
| /* A packet is lost if it has not been s/acked beyond |
| * the recent RTT plus the reordering window. |
| */ |
| remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd); |
| if (remaining <= 0) { |
| tcp_mark_skb_lost(sk, skb); |
| list_del_init(&skb->tcp_tsorted_anchor); |
| } else { |
| /* Record maximum wait time */ |
| *reo_timeout = max_t(u32, *reo_timeout, remaining); |
| } |
| } |
| } |
| |
| bool tcp_rack_mark_lost(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 timeout; |
| |
| if (!tp->rack.advanced) |
| return false; |
| |
| /* Reset the advanced flag to avoid unnecessary queue scanning */ |
| tp->rack.advanced = 0; |
| tcp_rack_detect_loss(sk, &timeout); |
| if (timeout) { |
| timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN; |
| inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, |
| timeout, inet_csk(sk)->icsk_rto); |
| } |
| return !!timeout; |
| } |
| |
| /* Record the most recently (re)sent time among the (s)acked packets |
| * This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from |
| * draft-cheng-tcpm-rack-00.txt |
| */ |
| void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq, |
| u64 xmit_time) |
| { |
| u32 rtt_us; |
| |
| rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time); |
| if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) { |
| /* If the sacked packet was retransmitted, it's ambiguous |
| * whether the retransmission or the original (or the prior |
| * retransmission) was sacked. |
| * |
| * If the original is lost, there is no ambiguity. Otherwise |
| * we assume the original can be delayed up to aRTT + min_rtt. |
| * the aRTT term is bounded by the fast recovery or timeout, |
| * so it's at least one RTT (i.e., retransmission is at least |
| * an RTT later). |
| */ |
| return; |
| } |
| tp->rack.advanced = 1; |
| tp->rack.rtt_us = rtt_us; |
| if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp, |
| end_seq, tp->rack.end_seq)) { |
| tp->rack.mstamp = xmit_time; |
| tp->rack.end_seq = end_seq; |
| } |
| } |
| |
| /* We have waited long enough to accommodate reordering. Mark the expired |
| * packets lost and retransmit them. |
| */ |
| void tcp_rack_reo_timeout(struct sock *sk) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| u32 timeout, prior_inflight; |
| u32 lost = tp->lost; |
| |
| prior_inflight = tcp_packets_in_flight(tp); |
| tcp_rack_detect_loss(sk, &timeout); |
| if (prior_inflight != tcp_packets_in_flight(tp)) { |
| if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) { |
| tcp_enter_recovery(sk, false); |
| if (!inet_csk(sk)->icsk_ca_ops->cong_control) |
| tcp_cwnd_reduction(sk, 1, tp->lost - lost, 0); |
| } |
| tcp_xmit_retransmit_queue(sk); |
| } |
| if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) |
| tcp_rearm_rto(sk); |
| } |
| |
| /* Updates the RACK's reo_wnd based on DSACK and no. of recoveries. |
| * |
| * If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded |
| * by srtt), since there is possibility that spurious retransmission was |
| * due to reordering delay longer than reo_wnd. |
| * |
| * Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16) |
| * no. of successful recoveries (accounts for full DSACK-based loss |
| * recovery undo). After that, reset it to default (min_rtt/4). |
| * |
| * At max, reo_wnd is incremented only once per rtt. So that the new |
| * DSACK on which we are reacting, is due to the spurious retx (approx) |
| * after the reo_wnd has been updated last time. |
| * |
| * reo_wnd is tracked in terms of steps (of min_rtt/4), rather than |
| * absolute value to account for change in rtt. |
| */ |
| void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs) |
| { |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND || |
| !rs->prior_delivered) |
| return; |
| |
| /* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */ |
| if (before(rs->prior_delivered, tp->rack.last_delivered)) |
| tp->rack.dsack_seen = 0; |
| |
| /* Adjust the reo_wnd if update is pending */ |
| if (tp->rack.dsack_seen) { |
| tp->rack.reo_wnd_steps = min_t(u32, 0xFF, |
| tp->rack.reo_wnd_steps + 1); |
| tp->rack.dsack_seen = 0; |
| tp->rack.last_delivered = tp->delivered; |
| tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH; |
| } else if (!tp->rack.reo_wnd_persist) { |
| tp->rack.reo_wnd_steps = 1; |
| } |
| } |
| |
| /* RFC6582 NewReno recovery for non-SACK connection. It simply retransmits |
| * the next unacked packet upon receiving |
| * a) three or more DUPACKs to start the fast recovery |
| * b) an ACK acknowledging new data during the fast recovery. |
| */ |
| void tcp_newreno_mark_lost(struct sock *sk, bool snd_una_advanced) |
| { |
| const u8 state = inet_csk(sk)->icsk_ca_state; |
| struct tcp_sock *tp = tcp_sk(sk); |
| |
| if ((state < TCP_CA_Recovery && tp->sacked_out >= tp->reordering) || |
| (state == TCP_CA_Recovery && snd_una_advanced)) { |
| struct sk_buff *skb = tcp_rtx_queue_head(sk); |
| u32 mss; |
| |
| if (TCP_SKB_CB(skb)->sacked & TCPCB_LOST) |
| return; |
| |
| mss = tcp_skb_mss(skb); |
| if (tcp_skb_pcount(skb) > 1 && skb->len > mss) |
| tcp_fragment(sk, TCP_FRAG_IN_RTX_QUEUE, skb, |
| mss, mss, GFP_ATOMIC); |
| |
| tcp_mark_skb_lost(sk, skb); |
| } |
| } |