diff options
Diffstat (limited to 'net/ipv4/tcp_recovery.c')
| -rw-r--r-- | net/ipv4/tcp_recovery.c | 237 |
1 files changed, 237 insertions, 0 deletions
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c new file mode 100644 index 000000000..c08579369 --- /dev/null +++ b/net/ipv4/tcp_recovery.c @@ -0,0 +1,237 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/tcp.h> +#include <net/tcp.h> + +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 && + !(READ_ONCE(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_skb_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_US); + 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_skb_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 a DSACK is received that seems like it may have been due to reordering + * triggering fast recovery, 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 ((READ_ONCE(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); + } +} |