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-rw-r--r--Documentation/networking/ip-sysctl.txt18
-rw-r--r--include/linux/tcp.h3
-rw-r--r--net/ipv4/tcp_input.c73
3 files changed, 68 insertions, 26 deletions
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 8a977a0aaede..f98ca633b528 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -225,19 +225,13 @@ tcp_fin_timeout - INTEGER
Default: 60 seconds
tcp_frto - INTEGER
- Enables Forward RTO-Recovery (F-RTO) defined in RFC4138.
+ Enables Forward RTO-Recovery (F-RTO) defined in RFC5682.
F-RTO is an enhanced recovery algorithm for TCP retransmission
- timeouts. It is particularly beneficial in wireless environments
- where packet loss is typically due to random radio interference
- rather than intermediate router congestion. F-RTO is sender-side
- only modification. Therefore it does not require any support from
- the peer.
-
- If set to 1, basic version is enabled. 2 enables SACK enhanced
- F-RTO if flow uses SACK. The basic version can be used also when
- SACK is in use though scenario(s) with it exists where F-RTO
- interacts badly with the packet counting of the SACK enabled TCP
- flow.
+ timeouts. It is particularly beneficial in networks where the
+ RTT fluctuates (e.g., wireless). F-RTO is sender-side only
+ modification. It does not require any support from the peer.
+
+ By default it's enabled with a non-zero value. 0 disables F-RTO.
tcp_keepalive_time - INTEGER
How often TCP sends out keepalive messages when keepalive is enabled.
diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index f5f203b36379..5adbc33d1ab3 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -192,7 +192,8 @@ struct tcp_sock {
u8 nonagle : 4,/* Disable Nagle algorithm? */
thin_lto : 1,/* Use linear timeouts for thin streams */
thin_dupack : 1,/* Fast retransmit on first dupack */
- repair : 1;
+ repair : 1,
+ frto : 1;/* F-RTO (RFC5682) activated in CA_Loss */
u8 repair_queue;
u8 do_early_retrans:1,/* Enable RFC5827 early-retransmit */
syn_data:1, /* SYN includes data */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8d821e45b917..b2b36196b342 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -107,6 +107,7 @@ int sysctl_tcp_early_retrans __read_mostly = 3;
#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_ORIG_SACK_ACKED 0x200 /* Never retransmitted data are (s)acked */
#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_SACK_RENEGING 0x2000 /* snd_una advanced to a sacked seq */
@@ -1155,6 +1156,8 @@ static u8 tcp_sacktag_one(struct sock *sk,
tcp_highest_sack_seq(tp)))
state->reord = min(fack_count,
state->reord);
+ if (!after(end_seq, tp->high_seq))
+ state->flag |= FLAG_ORIG_SACK_ACKED;
}
if (sacked & TCPCB_LOST) {
@@ -1835,10 +1838,13 @@ void tcp_enter_loss(struct sock *sk, int how)
const struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
+ bool new_recovery = false;
/* Reduce ssthresh if it has not yet been made inside this window. */
- if (icsk->icsk_ca_state <= TCP_CA_Disorder || tp->snd_una == tp->high_seq ||
+ if (icsk->icsk_ca_state <= TCP_CA_Disorder ||
+ !after(tp->high_seq, tp->snd_una) ||
(icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
+ new_recovery = true;
tp->prior_ssthresh = tcp_current_ssthresh(sk);
tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
tcp_ca_event(sk, CA_EVENT_LOSS);
@@ -1883,6 +1889,14 @@ void tcp_enter_loss(struct sock *sk, int how)
tcp_set_ca_state(sk, TCP_CA_Loss);
tp->high_seq = tp->snd_nxt;
TCP_ECN_queue_cwr(tp);
+
+ /* F-RTO RFC5682 sec 3.1 step 1: retransmit SND.UNA if no previous
+ * loss recovery is underway except recurring timeout(s) on
+ * the same SND.UNA (sec 3.2). Disable F-RTO on path MTU probing
+ */
+ tp->frto = sysctl_tcp_frto &&
+ (new_recovery || icsk->icsk_retransmits) &&
+ !inet_csk(sk)->icsk_mtup.probe_size;
}
/* If ACK arrived pointing to a remembered SACK, it means that our
@@ -2426,12 +2440,12 @@ static int tcp_try_undo_partial(struct sock *sk, int acked)
return failed;
}
-/* Undo during loss recovery after partial ACK. */
-static bool tcp_try_undo_loss(struct sock *sk)
+/* Undo during loss recovery after partial ACK or using F-RTO. */
+static bool tcp_try_undo_loss(struct sock *sk, bool frto_undo)
{
struct tcp_sock *tp = tcp_sk(sk);
- if (tcp_may_undo(tp)) {
+ if (frto_undo || tcp_may_undo(tp)) {
struct sk_buff *skb;
tcp_for_write_queue(skb, sk) {
if (skb == tcp_send_head(sk))
@@ -2445,9 +2459,12 @@ static bool tcp_try_undo_loss(struct sock *sk)
tp->lost_out = 0;
tcp_undo_cwr(sk, true);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
+ if (frto_undo)
+ NET_INC_STATS_BH(sock_net(sk),
+ LINUX_MIB_TCPSPURIOUSRTOS);
inet_csk(sk)->icsk_retransmits = 0;
tp->undo_marker = 0;
- if (tcp_is_sack(tp))
+ if (frto_undo || tcp_is_sack(tp))
tcp_set_ca_state(sk, TCP_CA_Open);
return true;
}
@@ -2667,24 +2684,52 @@ static void tcp_enter_recovery(struct sock *sk, bool ece_ack)
/* Process an ACK in CA_Loss state. Move to CA_Open if lost data are
* recovered or spurious. Otherwise retransmits more on partial ACKs.
*/
-static void tcp_process_loss(struct sock *sk, int flag)
+static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
{
struct inet_connection_sock *icsk = inet_csk(sk);
struct tcp_sock *tp = tcp_sk(sk);
+ bool recovered = !before(tp->snd_una, tp->high_seq);
- if (!before(tp->snd_una, tp->high_seq)) {
+ if (tp->frto) { /* F-RTO RFC5682 sec 3.1 (sack enhanced version). */
+ if (flag & FLAG_ORIG_SACK_ACKED) {
+ /* Step 3.b. A timeout is spurious if not all data are
+ * lost, i.e., never-retransmitted data are (s)acked.
+ */
+ tcp_try_undo_loss(sk, true);
+ return;
+ }
+ if (after(tp->snd_nxt, tp->high_seq) &&
+ (flag & FLAG_DATA_SACKED || is_dupack)) {
+ tp->frto = 0; /* Loss was real: 2nd part of step 3.a */
+ } else if (flag & FLAG_SND_UNA_ADVANCED && !recovered) {
+ tp->high_seq = tp->snd_nxt;
+ __tcp_push_pending_frames(sk, tcp_current_mss(sk),
+ TCP_NAGLE_OFF);
+ if (after(tp->snd_nxt, tp->high_seq))
+ return; /* Step 2.b */
+ tp->frto = 0;
+ }
+ }
+
+ if (recovered) {
+ /* F-RTO RFC5682 sec 3.1 step 2.a and 1st part of step 3.a */
icsk->icsk_retransmits = 0;
tcp_try_undo_recovery(sk);
return;
}
-
if (flag & FLAG_DATA_ACKED)
icsk->icsk_retransmits = 0;
- if (tcp_is_reno(tp) && flag & FLAG_SND_UNA_ADVANCED)
- tcp_reset_reno_sack(tp);
- if (tcp_try_undo_loss(sk))
+ if (tcp_is_reno(tp)) {
+ /* A Reno DUPACK means new data in F-RTO step 2.b above are
+ * delivered. Lower inflight to clock out (re)tranmissions.
+ */
+ if (after(tp->snd_nxt, tp->high_seq) && is_dupack)
+ tcp_add_reno_sack(sk);
+ else if (flag & FLAG_SND_UNA_ADVANCED)
+ tcp_reset_reno_sack(tp);
+ }
+ if (tcp_try_undo_loss(sk, false))
return;
- tcp_moderate_cwnd(tp);
tcp_xmit_retransmit_queue(sk);
}
@@ -2764,7 +2809,7 @@ static void tcp_fastretrans_alert(struct sock *sk, int pkts_acked,
newly_acked_sacked = pkts_acked + tp->sacked_out - prior_sacked;
break;
case TCP_CA_Loss:
- tcp_process_loss(sk, flag);
+ tcp_process_loss(sk, flag, is_dupack);
if (icsk->icsk_ca_state != TCP_CA_Open)
return;
/* Fall through to processing in Open state. */
@@ -3003,6 +3048,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
}
if (!(sacked & TCPCB_SACKED_ACKED))
reord = min(pkts_acked, reord);
+ if (!after(scb->end_seq, tp->high_seq))
+ flag |= FLAG_ORIG_SACK_ACKED;
}
if (sacked & TCPCB_SACKED_ACKED)
Copyright © 1996 – 2023 Jason A. Donenfeld. All Rights Reverse Engineered.