diff options
Diffstat (limited to 'net/ipv4/tcp_recovery.c')
-rw-r--r-- | net/ipv4/tcp_recovery.c | 149 |
1 files changed, 112 insertions, 37 deletions
diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c index e36df4fcfeba..d8acbd9f477a 100644 --- a/net/ipv4/tcp_recovery.c +++ b/net/ipv4/tcp_recovery.c @@ -1,9 +1,33 @@ #include <linux/tcp.h> #include <net/tcp.h> -int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOST_RETRANS; +int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOSS_DETECTION; -/* Marks a packet lost, if some packet sent later has been (s)acked. +static void tcp_rack_mark_skb_lost(struct sock *sk, struct sk_buff *skb) +{ + struct tcp_sock *tp = tcp_sk(sk); + + tcp_skb_mark_lost_uncond_verify(tp, skb); + if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) { + /* Account for retransmits that are lost again */ + TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS; + tp->retrans_out -= tcp_skb_pcount(skb); + NET_ADD_STATS(sock_net(sk), LINUX_MIB_TCPLOSTRETRANSMIT, + tcp_skb_pcount(skb)); + } +} + +static bool tcp_rack_sent_after(const struct skb_mstamp *t1, + const struct skb_mstamp *t2, + u32 seq1, u32 seq2) +{ + return skb_mstamp_after(t1, t2) || + (t1->v64 == t2->v64 && after(seq1, seq2)); +} + +/* 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: * @@ -16,31 +40,26 @@ int sysctl_tcp_recovery __read_mostly = TCP_RACK_LOST_RETRANS; * is being more resilient to reordering by simply allowing some * "settling delay", instead of tweaking the dupthresh. * - * The current version is only used after recovery starts but can be - * easily extended to detect the first loss. + * 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. */ -int tcp_rack_mark_lost(struct sock *sk) +static void tcp_rack_detect_loss(struct sock *sk, const struct skb_mstamp *now, + u32 *reo_timeout) { struct tcp_sock *tp = tcp_sk(sk); struct sk_buff *skb; - u32 reo_wnd, prior_retrans = tp->retrans_out; - - if (inet_csk(sk)->icsk_ca_state < TCP_CA_Recovery || !tp->rack.advanced) - return 0; - - /* Reset the advanced flag to avoid unnecessary queue scanning */ - tp->rack.advanced = 0; + u32 reo_wnd; + *reo_timeout = 0; /* To be more reordering resilient, allow min_rtt/4 settling delay * (lower-bounded to 1000uS). We use min_rtt instead of the smoothed * RTT because reordering is often a path property and less related * to queuing or delayed ACKs. - * - * TODO: measure and adapt to the observed reordering delay, and - * use a timer to retransmit like the delayed early retransmit. */ reo_wnd = 1000; - if (tp->rack.reord && tcp_min_rtt(tp) != ~0U) + if ((tp->rack.reord || !tp->lost_out) && tcp_min_rtt(tp) != ~0U) reo_wnd = max(tcp_min_rtt(tp) >> 2, reo_wnd); tcp_for_write_queue(skb, sk) { @@ -54,20 +73,29 @@ int tcp_rack_mark_lost(struct sock *sk) scb->sacked & TCPCB_SACKED_ACKED) continue; - if (skb_mstamp_after(&tp->rack.mstamp, &skb->skb_mstamp)) { + if (tcp_rack_sent_after(&tp->rack.mstamp, &skb->skb_mstamp, + tp->rack.end_seq, scb->end_seq)) { + /* Step 3 in draft-cheng-tcpm-rack-00.txt: + * A packet is lost if its elapsed time is beyond + * the recent RTT plus the reordering window. + */ + u32 elapsed = skb_mstamp_us_delta(now, + &skb->skb_mstamp); + s32 remaining = tp->rack.rtt_us + reo_wnd - elapsed; - if (skb_mstamp_us_delta(&tp->rack.mstamp, - &skb->skb_mstamp) <= reo_wnd) + if (remaining < 0) { + tcp_rack_mark_skb_lost(sk, skb); continue; - - /* skb is lost if packet sent later is sacked */ - tcp_skb_mark_lost_uncond_verify(tp, skb); - if (scb->sacked & TCPCB_SACKED_RETRANS) { - scb->sacked &= ~TCPCB_SACKED_RETRANS; - tp->retrans_out -= tcp_skb_pcount(skb); - NET_INC_STATS(sock_net(sk), - LINUX_MIB_TCPLOSTRETRANSMIT); } + + /* Skip ones marked lost but not yet retransmitted */ + if ((scb->sacked & TCPCB_LOST) && + !(scb->sacked & TCPCB_SACKED_RETRANS)) + continue; + + /* Record maximum wait time (+1 to avoid 0) */ + *reo_timeout = max_t(u32, *reo_timeout, 1 + remaining); + } else if (!(scb->sacked & TCPCB_RETRANS)) { /* Original data are sent sequentially so stop early * b/c the rest are all sent after rack_sent @@ -75,20 +103,43 @@ int tcp_rack_mark_lost(struct sock *sk) break; } } - return prior_retrans - tp->retrans_out; } -/* Record the most recently (re)sent time among the (s)acked packets */ -void tcp_rack_advance(struct tcp_sock *tp, - const struct skb_mstamp *xmit_time, u8 sacked) +void tcp_rack_mark_lost(struct sock *sk, const struct skb_mstamp *now) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 timeout; + + if (!tp->rack.advanced) + return; + + /* Reset the advanced flag to avoid unnecessary queue scanning */ + tp->rack.advanced = 0; + tcp_rack_detect_loss(sk, now, &timeout); + if (timeout) { + timeout = usecs_to_jiffies(timeout + TCP_REO_TIMEOUT_MIN); + inet_csk_reset_xmit_timer(sk, ICSK_TIME_REO_TIMEOUT, + timeout, inet_csk(sk)->icsk_rto); + } +} + +/* 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, + const struct skb_mstamp *xmit_time, + const struct skb_mstamp *ack_time) { + u32 rtt_us; + if (tp->rack.mstamp.v64 && - !skb_mstamp_after(xmit_time, &tp->rack.mstamp)) + !tcp_rack_sent_after(xmit_time, &tp->rack.mstamp, + end_seq, tp->rack.end_seq)) return; + rtt_us = skb_mstamp_us_delta(ack_time, xmit_time); if (sacked & TCPCB_RETRANS) { - struct skb_mstamp now; - /* If the sacked packet was retransmitted, it's ambiguous * whether the retransmission or the original (or the prior * retransmission) was sacked. @@ -99,11 +150,35 @@ void tcp_rack_advance(struct tcp_sock *tp, * so it's at least one RTT (i.e., retransmission is at least * an RTT later). */ - skb_mstamp_get(&now); - if (skb_mstamp_us_delta(&now, xmit_time) < tcp_min_rtt(tp)) + if (rtt_us < tcp_min_rtt(tp)) return; } - + tp->rack.rtt_us = rtt_us; tp->rack.mstamp = *xmit_time; + tp->rack.end_seq = end_seq; tp->rack.advanced = 1; } + +/* 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); + struct skb_mstamp now; + u32 timeout, prior_inflight; + + skb_mstamp_get(&now); + prior_inflight = tcp_packets_in_flight(tp); + tcp_rack_detect_loss(sk, &now, &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, 0); + } + tcp_xmit_retransmit_queue(sk); + } + if (inet_csk(sk)->icsk_pending != ICSK_TIME_RETRANS) + tcp_rearm_rto(sk); +} |