int sysctl_tcp_rfc1337 __read_mostly;
int sysctl_tcp_max_orphans __read_mostly = NR_FILE;
int sysctl_tcp_frto __read_mostly = 2;
-int sysctl_tcp_frto_response __read_mostly;
int sysctl_tcp_thin_dupack __read_mostly;
#define FLAG_DATA_SACKED 0x20 /* New SACK. */
#define FLAG_ECE 0x40 /* ECE in this ACK */
#define FLAG_SLOWPATH 0x100 /* Do not skip RFC checks for window update.*/
-#define FLAG_ONLY_ORIG_SACKED 0x200 /* SACKs only non-rexmit sent before RTO */
#define FLAG_SND_UNA_ADVANCED 0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */
#define FLAG_DSACKING_ACK 0x800 /* SACK blocks contained D-SACK info */
-#define FLAG_NONHEAD_RETRANS_ACKED 0x1000 /* Non-head rexmitted data was ACKed */
#define FLAG_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
#define FLAG_ACKED (FLAG_DATA_ACKED|FLAG_SYN_ACKED)
#define FLAG_NOT_DUP (FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
#define FLAG_CA_ALERT (FLAG_DATA_SACKED|FLAG_ECE)
#define FLAG_FORWARD_PROGRESS (FLAG_ACKED|FLAG_DATA_SACKED)
-#define FLAG_ANY_PROGRESS (FLAG_FORWARD_PROGRESS|FLAG_SND_UNA_ADVANCED)
#define TCP_REMNANT (TCP_FLAG_FIN|TCP_FLAG_URG|TCP_FLAG_SYN|TCP_FLAG_PSH)
#define TCP_HP_BITS (~(TCP_RESERVED_BITS|TCP_FLAG_PSH))
tcp_highest_sack_seq(tp)))
state->reord = min(fack_count,
state->reord);
-
- /* SACK enhanced F-RTO (RFC4138; Appendix B) */
- if (!after(end_seq, tp->frto_highmark))
- state->flag |= FLAG_ONLY_ORIG_SACKED;
}
if (sacked & TCPCB_LOST) {
tcp_sacktag_write_queue(struct sock *sk, const struct sk_buff *ack_skb,
u32 prior_snd_una)
{
- const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
const unsigned char *ptr = (skb_transport_header(ack_skb) +
TCP_SKB_CB(ack_skb)->sacked);
start_seq, end_seq, dup_sack);
advance_sp:
- /* SACK enhanced FRTO (RFC4138, Appendix B): Clearing correct
- * due to in-order walk
- */
- if (after(end_seq, tp->frto_highmark))
- state.flag &= ~FLAG_ONLY_ORIG_SACKED;
-
i++;
}
tcp_verify_left_out(tp);
if ((state.reord < tp->fackets_out) &&
- ((icsk->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker) &&
- (!tp->frto_highmark || after(tp->snd_una, tp->frto_highmark)))
+ ((inet_csk(sk)->icsk_ca_state != TCP_CA_Loss) || tp->undo_marker))
tcp_update_reordering(sk, tp->fackets_out - state.reord, 0);
out:
tp->sacked_out = 0;
}
-static int tcp_is_sackfrto(const struct tcp_sock *tp)
-{
- return (sysctl_tcp_frto == 0x2) && !tcp_is_reno(tp);
-}
-
-/* F-RTO can only be used if TCP has never retransmitted anything other than
- * head (SACK enhanced variant from Appendix B of RFC4138 is more robust here)
- */
-bool tcp_use_frto(struct sock *sk)
-{
- const struct tcp_sock *tp = tcp_sk(sk);
- const struct inet_connection_sock *icsk = inet_csk(sk);
- struct sk_buff *skb;
-
- if (!sysctl_tcp_frto)
- return false;
-
- /* MTU probe and F-RTO won't really play nicely along currently */
- if (icsk->icsk_mtup.probe_size)
- return false;
-
- if (tcp_is_sackfrto(tp))
- return true;
-
- /* Avoid expensive walking of rexmit queue if possible */
- if (tp->retrans_out > 1)
- return false;
-
- skb = tcp_write_queue_head(sk);
- if (tcp_skb_is_last(sk, skb))
- return true;
- skb = tcp_write_queue_next(sk, skb); /* Skips head */
- tcp_for_write_queue_from(skb, sk) {
- if (skb == tcp_send_head(sk))
- break;
- if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
- return false;
- /* Short-circuit when first non-SACKed skb has been checked */
- if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED))
- break;
- }
- return true;
-}
-
-/* RTO occurred, but do not yet enter Loss state. Instead, defer RTO
- * recovery a bit and use heuristics in tcp_process_frto() to detect if
- * the RTO was spurious. Only clear SACKED_RETRANS of the head here to
- * keep retrans_out counting accurate (with SACK F-RTO, other than head
- * may still have that bit set); TCPCB_LOST and remaining SACKED_RETRANS
- * bits are handled if the Loss state is really to be entered (in
- * tcp_enter_frto_loss).
- *
- * Do like tcp_enter_loss() would; when RTO expires the second time it
- * does:
- * "Reduce ssthresh if it has not yet been made inside this window."
- */
-void tcp_enter_frto(struct sock *sk)
-{
- const struct inet_connection_sock *icsk = inet_csk(sk);
- struct tcp_sock *tp = tcp_sk(sk);
- struct sk_buff *skb;
-
- if ((!tp->frto_counter && icsk->icsk_ca_state <= TCP_CA_Disorder) ||
- tp->snd_una == tp->high_seq ||
- ((icsk->icsk_ca_state == TCP_CA_Loss || tp->frto_counter) &&
- !icsk->icsk_retransmits)) {
- tp->prior_ssthresh = tcp_current_ssthresh(sk);
- /* Our state is too optimistic in ssthresh() call because cwnd
- * is not reduced until tcp_enter_frto_loss() when previous F-RTO
- * recovery has not yet completed. Pattern would be this: RTO,
- * Cumulative ACK, RTO (2xRTO for the same segment does not end
- * up here twice).
- * RFC4138 should be more specific on what to do, even though
- * RTO is quite unlikely to occur after the first Cumulative ACK
- * due to back-off and complexity of triggering events ...
- */
- if (tp->frto_counter) {
- u32 stored_cwnd;
- stored_cwnd = tp->snd_cwnd;
- tp->snd_cwnd = 2;
- tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
- tp->snd_cwnd = stored_cwnd;
- } else {
- tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
- }
- /* ... in theory, cong.control module could do "any tricks" in
- * ssthresh(), which means that ca_state, lost bits and lost_out
- * counter would have to be faked before the call occurs. We
- * consider that too expensive, unlikely and hacky, so modules
- * using these in ssthresh() must deal these incompatibility
- * issues if they receives CA_EVENT_FRTO and frto_counter != 0
- */
- tcp_ca_event(sk, CA_EVENT_FRTO);
- }
-
- tp->undo_marker = tp->snd_una;
- tp->undo_retrans = 0;
-
- skb = tcp_write_queue_head(sk);
- if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
- tp->undo_marker = 0;
- if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS) {
- TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
- tp->retrans_out -= tcp_skb_pcount(skb);
- }
- tcp_verify_left_out(tp);
-
- /* Too bad if TCP was application limited */
- tp->snd_cwnd = min(tp->snd_cwnd, tcp_packets_in_flight(tp) + 1);
-
- /* Earlier loss recovery underway (see RFC4138; Appendix B).
- * The last condition is necessary at least in tp->frto_counter case.
- */
- if (tcp_is_sackfrto(tp) && (tp->frto_counter ||
- ((1 << icsk->icsk_ca_state) & (TCPF_CA_Recovery|TCPF_CA_Loss))) &&
- after(tp->high_seq, tp->snd_una)) {
- tp->frto_highmark = tp->high_seq;
- } else {
- tp->frto_highmark = tp->snd_nxt;
- }
- tcp_set_ca_state(sk, TCP_CA_Disorder);
- tp->high_seq = tp->snd_nxt;
- tp->frto_counter = 1;
-}
-
-/* Enter Loss state after F-RTO was applied. Dupack arrived after RTO,
- * which indicates that we should follow the traditional RTO recovery,
- * i.e. mark everything lost and do go-back-N retransmission.
- */
-static void tcp_enter_frto_loss(struct sock *sk, int allowed_segments, int flag)
-{
- struct tcp_sock *tp = tcp_sk(sk);
- struct sk_buff *skb;
-
- tp->lost_out = 0;
- tp->retrans_out = 0;
- if (tcp_is_reno(tp))
- tcp_reset_reno_sack(tp);
-
- tcp_for_write_queue(skb, sk) {
- if (skb == tcp_send_head(sk))
- break;
-
- TCP_SKB_CB(skb)->sacked &= ~TCPCB_LOST;
- /*
- * Count the retransmission made on RTO correctly (only when
- * waiting for the first ACK and did not get it)...
- */
- if ((tp->frto_counter == 1) && !(flag & FLAG_DATA_ACKED)) {
- /* For some reason this R-bit might get cleared? */
- if (TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_RETRANS)
- tp->retrans_out += tcp_skb_pcount(skb);
- /* ...enter this if branch just for the first segment */
- flag |= FLAG_DATA_ACKED;
- } else {
- if (TCP_SKB_CB(skb)->sacked & TCPCB_RETRANS)
- tp->undo_marker = 0;
- TCP_SKB_CB(skb)->sacked &= ~TCPCB_SACKED_RETRANS;
- }
-
- /* Marking forward transmissions that were made after RTO lost
- * can cause unnecessary retransmissions in some scenarios,
- * SACK blocks will mitigate that in some but not in all cases.
- * We used to not mark them but it was causing break-ups with
- * receivers that do only in-order receival.
- *
- * TODO: we could detect presence of such receiver and select
- * different behavior per flow.
- */
- if (!(TCP_SKB_CB(skb)->sacked & TCPCB_SACKED_ACKED)) {
- TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
- tp->lost_out += tcp_skb_pcount(skb);
- tp->retransmit_high = TCP_SKB_CB(skb)->end_seq;
- }
- }
- tcp_verify_left_out(tp);
-
- tp->snd_cwnd = tcp_packets_in_flight(tp) + allowed_segments;
- tp->snd_cwnd_cnt = 0;
- tp->snd_cwnd_stamp = tcp_time_stamp;
- tp->frto_counter = 0;
-
- tp->reordering = min_t(unsigned int, tp->reordering,
- sysctl_tcp_reordering);
- tcp_set_ca_state(sk, TCP_CA_Loss);
- tp->high_seq = tp->snd_nxt;
- TCP_ECN_queue_cwr(tp);
-
- tcp_clear_all_retrans_hints(tp);
-}
-
static void tcp_clear_retrans_partial(struct tcp_sock *tp)
{
tp->retrans_out = 0;
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->snd_nxt;
TCP_ECN_queue_cwr(tp);
- /* Abort F-RTO algorithm if one is in progress */
- tp->frto_counter = 0;
}
/* If ACK arrived pointing to a remembered SACK, it means that our
struct tcp_sock *tp = tcp_sk(sk);
__u32 packets_out;
- /* Do not perform any recovery during F-RTO algorithm */
- if (tp->frto_counter)
- return false;
-
/* Trick#1: The loss is proven. */
if (tp->lost_out)
return true;
tcp_verify_left_out(tp);
- if (!tp->frto_counter && !tcp_any_retrans_done(sk))
+ if (!tcp_any_retrans_done(sk))
tp->retrans_stamp = 0;
if (flag & FLAG_ECE)
flag |= FLAG_RETRANS_DATA_ACKED;
ca_seq_rtt = -1;
seq_rtt = -1;
- if ((flag & FLAG_DATA_ACKED) || (acked_pcount > 1))
- flag |= FLAG_NONHEAD_RETRANS_ACKED;
} else {
ca_seq_rtt = now - scb->when;
last_ackt = skb->tstamp;
return flag;
}
-/* A very conservative spurious RTO response algorithm: reduce cwnd and
- * continue in congestion avoidance.
- */
-static void tcp_conservative_spur_to_response(struct tcp_sock *tp)
-{
- tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
- tp->snd_cwnd_cnt = 0;
- TCP_ECN_queue_cwr(tp);
- tcp_moderate_cwnd(tp);
-}
-
-/* A conservative spurious RTO response algorithm: reduce cwnd using
- * PRR and continue in congestion avoidance.
- */
-static void tcp_cwr_spur_to_response(struct sock *sk)
-{
- tcp_enter_cwr(sk, 0);
-}
-
-static void tcp_undo_spur_to_response(struct sock *sk, int flag)
-{
- if (flag & FLAG_ECE)
- tcp_cwr_spur_to_response(sk);
- else
- tcp_undo_cwr(sk, true);
-}
-
-/* F-RTO spurious RTO detection algorithm (RFC4138)
- *
- * F-RTO affects during two new ACKs following RTO (well, almost, see inline
- * comments). State (ACK number) is kept in frto_counter. When ACK advances
- * window (but not to or beyond highest sequence sent before RTO):
- * On First ACK, send two new segments out.
- * On Second ACK, RTO was likely spurious. Do spurious response (response
- * algorithm is not part of the F-RTO detection algorithm
- * given in RFC4138 but can be selected separately).
- * Otherwise (basically on duplicate ACK), RTO was (likely) caused by a loss
- * and TCP falls back to conventional RTO recovery. F-RTO allows overriding
- * of Nagle, this is done using frto_counter states 2 and 3, when a new data
- * segment of any size sent during F-RTO, state 2 is upgraded to 3.
- *
- * Rationale: if the RTO was spurious, new ACKs should arrive from the
- * original window even after we transmit two new data segments.
- *
- * SACK version:
- * on first step, wait until first cumulative ACK arrives, then move to
- * the second step. In second step, the next ACK decides.
- *
- * F-RTO is implemented (mainly) in four functions:
- * - tcp_use_frto() is used to determine if TCP is can use F-RTO
- * - tcp_enter_frto() prepares TCP state on RTO if F-RTO is used, it is
- * called when tcp_use_frto() showed green light
- * - tcp_process_frto() handles incoming ACKs during F-RTO algorithm
- * - tcp_enter_frto_loss() is called if there is not enough evidence
- * to prove that the RTO is indeed spurious. It transfers the control
- * from F-RTO to the conventional RTO recovery
- */
-static bool tcp_process_frto(struct sock *sk, int flag)
-{
- struct tcp_sock *tp = tcp_sk(sk);
-
- tcp_verify_left_out(tp);
-
- /* Duplicate the behavior from Loss state (fastretrans_alert) */
- if (flag & FLAG_DATA_ACKED)
- inet_csk(sk)->icsk_retransmits = 0;
-
- if ((flag & FLAG_NONHEAD_RETRANS_ACKED) ||
- ((tp->frto_counter >= 2) && (flag & FLAG_RETRANS_DATA_ACKED)))
- tp->undo_marker = 0;
-
- if (!before(tp->snd_una, tp->frto_highmark)) {
- tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 2 : 3), flag);
- return true;
- }
-
- if (!tcp_is_sackfrto(tp)) {
- /* RFC4138 shortcoming in step 2; should also have case c):
- * ACK isn't duplicate nor advances window, e.g., opposite dir
- * data, winupdate
- */
- if (!(flag & FLAG_ANY_PROGRESS) && (flag & FLAG_NOT_DUP))
- return true;
-
- if (!(flag & FLAG_DATA_ACKED)) {
- tcp_enter_frto_loss(sk, (tp->frto_counter == 1 ? 0 : 3),
- flag);
- return true;
- }
- } else {
- if (!(flag & FLAG_DATA_ACKED) && (tp->frto_counter == 1)) {
- if (!tcp_packets_in_flight(tp)) {
- tcp_enter_frto_loss(sk, 2, flag);
- return true;
- }
-
- /* Prevent sending of new data. */
- tp->snd_cwnd = min(tp->snd_cwnd,
- tcp_packets_in_flight(tp));
- return true;
- }
-
- if ((tp->frto_counter >= 2) &&
- (!(flag & FLAG_FORWARD_PROGRESS) ||
- ((flag & FLAG_DATA_SACKED) &&
- !(flag & FLAG_ONLY_ORIG_SACKED)))) {
- /* RFC4138 shortcoming (see comment above) */
- if (!(flag & FLAG_FORWARD_PROGRESS) &&
- (flag & FLAG_NOT_DUP))
- return true;
-
- tcp_enter_frto_loss(sk, 3, flag);
- return true;
- }
- }
-
- if (tp->frto_counter == 1) {
- /* tcp_may_send_now needs to see updated state */
- tp->snd_cwnd = tcp_packets_in_flight(tp) + 2;
- tp->frto_counter = 2;
-
- if (!tcp_may_send_now(sk))
- tcp_enter_frto_loss(sk, 2, flag);
-
- return true;
- } else {
- switch (sysctl_tcp_frto_response) {
- case 2:
- tcp_undo_spur_to_response(sk, flag);
- break;
- case 1:
- tcp_conservative_spur_to_response(tp);
- break;
- default:
- tcp_cwr_spur_to_response(sk);
- break;
- }
- tp->frto_counter = 0;
- tp->undo_marker = 0;
- NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSPURIOUSRTOS);
- }
- return false;
-}
-
/* RFC 5961 7 [ACK Throttling] */
static void tcp_send_challenge_ack(struct sock *sk)
{
int prior_packets;
int prior_sacked = tp->sacked_out;
int pkts_acked = 0;
- bool frto_cwnd = false;
/* If the ack is older than previous acks
* then we can probably ignore it.
pkts_acked = prior_packets - tp->packets_out;
- if (tp->frto_counter)
- frto_cwnd = tcp_process_frto(sk, flag);
- /* Guarantee sacktag reordering detection against wrap-arounds */
- if (before(tp->frto_highmark, tp->snd_una))
- tp->frto_highmark = 0;
-
if (tcp_ack_is_dubious(sk, flag)) {
/* Advance CWND, if state allows this. */
- if ((flag & FLAG_DATA_ACKED) && !frto_cwnd &&
- tcp_may_raise_cwnd(sk, flag))
+ if ((flag & FLAG_DATA_ACKED) && tcp_may_raise_cwnd(sk, flag))
tcp_cong_avoid(sk, ack, prior_in_flight);
is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
tcp_fastretrans_alert(sk, pkts_acked, prior_sacked,
is_dupack, flag);
} else {
- if ((flag & FLAG_DATA_ACKED) && !frto_cwnd)
+ if (flag & FLAG_DATA_ACKED)
tcp_cong_avoid(sk, ack, prior_in_flight);
}
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