205 lines
6.6 KiB
C
205 lines
6.6 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/tcp.h>
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#include <net/tcp.h>
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static void tcp_rack_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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tcp_skb_mark_lost_uncond_verify(tp, skb);
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if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
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/* Account for retransmits that are lost again */
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TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
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tp->retrans_out -= tcp_skb_pcount(skb);
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NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT,
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tcp_skb_pcount(skb));
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}
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}
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static bool tcp_rack_sent_after(u64 t1, u64 t2, u32 seq1, u32 seq2)
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{
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return t1 > t2 || (t1 == t2 && after(seq1, seq2));
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}
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/* RACK loss detection (IETF draft draft-ietf-tcpm-rack-01):
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*
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* Marks a packet lost, if some packet sent later has been (s)acked.
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* The underlying idea is similar to the traditional dupthresh and FACK
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* but they look at different metrics:
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*
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* dupthresh: 3 OOO packets delivered (packet count)
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* FACK: sequence delta to highest sacked sequence (sequence space)
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* RACK: sent time delta to the latest delivered packet (time domain)
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*
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* The advantage of RACK is it applies to both original and retransmitted
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* packet and therefore is robust against tail losses. Another advantage
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* is being more resilient to reordering by simply allowing some
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* "settling delay", instead of tweaking the dupthresh.
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*
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* When tcp_rack_detect_loss() detects some packets are lost and we
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* are not already in the CA_Recovery state, either tcp_rack_reo_timeout()
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* or tcp_time_to_recover()'s "Trick#1: the loss is proven" code path will
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* make us enter the CA_Recovery state.
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*/
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static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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u32 min_rtt = tcp_min_rtt(tp);
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struct sk_buff *skb, *n;
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u32 reo_wnd;
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*reo_timeout = 0;
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/* To be more reordering resilient, allow min_rtt/4 settling delay
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* (lower-bounded to 1000uS). We use min_rtt instead of the smoothed
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* RTT because reordering is often a path property and less related
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* to queuing or delayed ACKs.
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*/
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reo_wnd = 1000;
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if ((tp->rack.reord || inet_csk(sk)->icsk_ca_state < TCP_CA_Recovery) &&
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min_rtt != ~0U) {
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reo_wnd = max((min_rtt >> 2) * tp->rack.reo_wnd_steps, reo_wnd);
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reo_wnd = min(reo_wnd, tp->srtt_us >> 3);
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}
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list_for_each_entry_safe(skb, n, &tp->tsorted_sent_queue,
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tcp_tsorted_anchor) {
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struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
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s32 remaining;
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/* Skip ones marked lost but not yet retransmitted */
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if ((scb->sacked & TCPCB_LOST) &&
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!(scb->sacked & TCPCB_SACKED_RETRANS))
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continue;
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if (!tcp_rack_sent_after(tp->rack.mstamp, skb->skb_mstamp,
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tp->rack.end_seq, scb->end_seq))
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break;
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/* A packet is lost if it has not been s/acked beyond
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* the recent RTT plus the reordering window.
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*/
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remaining = tp->rack.rtt_us + reo_wnd -
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tcp_stamp_us_delta(tp->tcp_mstamp, skb->skb_mstamp);
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if (remaining <= 0) {
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tcp_rack_mark_skb_lost(sk, skb);
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list_del_init(&skb->tcp_tsorted_anchor);
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} else {
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/* Record maximum wait time */
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*reo_timeout = max_t(u32, *reo_timeout, remaining);
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}
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}
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}
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void tcp_rack_mark_lost(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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u32 timeout;
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if (!tp->rack.advanced)
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return;
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/* Reset the advanced flag to avoid unnecessary queue scanning */
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tp->rack.advanced = 0;
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tcp_rack_detect_loss(sk, &timeout);
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if (timeout) {
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timeout = usecs_to_jiffies(timeout) + TCP_TIMEOUT_MIN;
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inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT,
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timeout, inet_csk(sk)->icsk_rto);
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}
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}
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/* Record the most recently (re)sent time among the (s)acked packets
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* This is "Step 3: Advance RACK.xmit_time and update RACK.RTT" from
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* draft-cheng-tcpm-rack-00.txt
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*/
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void tcp_rack_advance(struct tcp_sock *tp, u8 sacked, u32 end_seq,
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u64 xmit_time)
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{
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u32 rtt_us;
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rtt_us = tcp_stamp_us_delta(tp->tcp_mstamp, xmit_time);
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if (rtt_us < tcp_min_rtt(tp) && (sacked & TCPCB_RETRANS)) {
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/* If the sacked packet was retransmitted, it's ambiguous
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* whether the retransmission or the original (or the prior
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* retransmission) was sacked.
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*
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* If the original is lost, there is no ambiguity. Otherwise
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* we assume the original can be delayed up to aRTT + min_rtt.
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* the aRTT term is bounded by the fast recovery or timeout,
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* so it's at least one RTT (i.e., retransmission is at least
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* an RTT later).
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*/
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return;
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}
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tp->rack.advanced = 1;
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tp->rack.rtt_us = rtt_us;
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if (tcp_rack_sent_after(xmit_time, tp->rack.mstamp,
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end_seq, tp->rack.end_seq)) {
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tp->rack.mstamp = xmit_time;
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tp->rack.end_seq = end_seq;
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}
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}
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/* We have waited long enough to accommodate reordering. Mark the expired
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* packets lost and retransmit them.
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*/
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void tcp_rack_reo_timeout(struct sock *sk)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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u32 timeout, prior_inflight;
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prior_inflight = tcp_packets_in_flight(tp);
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tcp_rack_detect_loss(sk, &timeout);
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if (prior_inflight != tcp_packets_in_flight(tp)) {
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if (inet_csk(sk)->icsk_ca_state != TCP_CA_Recovery) {
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tcp_enter_recovery(sk, false);
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if (!inet_csk(sk)->icsk_ca_ops->cong_control)
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tcp_cwnd_reduction(sk, 1, 0);
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}
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tcp_xmit_retransmit_queue(sk);
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}
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if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS)
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tcp_rearm_rto(sk);
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}
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/* Updates the RACK's reo_wnd based on DSACK and no. of recoveries.
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*
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* If DSACK is received, increment reo_wnd by min_rtt/4 (upper bounded
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* by srtt), since there is possibility that spurious retransmission was
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* due to reordering delay longer than reo_wnd.
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*
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* Persist the current reo_wnd value for TCP_RACK_RECOVERY_THRESH (16)
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* no. of successful recoveries (accounts for full DSACK-based loss
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* recovery undo). After that, reset it to default (min_rtt/4).
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*
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* At max, reo_wnd is incremented only once per rtt. So that the new
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* DSACK on which we are reacting, is due to the spurious retx (approx)
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* after the reo_wnd has been updated last time.
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*
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* reo_wnd is tracked in terms of steps (of min_rtt/4), rather than
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* absolute value to account for change in rtt.
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*/
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void tcp_rack_update_reo_wnd(struct sock *sk, struct rate_sample *rs)
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{
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struct tcp_sock *tp = tcp_sk(sk);
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if (sock_net(sk)->ipv4.sysctl_tcp_recovery & TCP_RACK_STATIC_REO_WND ||
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!rs->prior_delivered)
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return;
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/* Disregard DSACK if a rtt has not passed since we adjusted reo_wnd */
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if (before(rs->prior_delivered, tp->rack.last_delivered))
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tp->rack.dsack_seen = 0;
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/* Adjust the reo_wnd if update is pending */
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if (tp->rack.dsack_seen) {
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tp->rack.reo_wnd_steps = min_t(u32, 0xFF,
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tp->rack.reo_wnd_steps + 1);
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tp->rack.dsack_seen = 0;
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tp->rack.last_delivered = tp->delivered;
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tp->rack.reo_wnd_persist = TCP_RACK_RECOVERY_THRESH;
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} else if (!tp->rack.reo_wnd_persist) {
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tp->rack.reo_wnd_steps = 1;
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}
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}
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