2 files changed, 98 insertions, 52 deletions

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index b386361ba3e8..d909feeeaea2 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -256,6 +256,7 @@ struct tcp_sock {
 	u32	prr_delivered;	/* Number of newly delivered packets to
 				 * receiver in Recovery. */
 	u32	prr_out;	/* Total number of pkts sent during Recovery. */
+	u32	delivered;	/* Total data packets delivered incl. rexmits */
 
  	u32	rcv_wnd;	/* Current receiver window		*/
 	u32	write_seq;	/* Tail(+1) of data held in tcp send buffer */
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 8194a250a01e..596c1cb6759a 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -126,6 +126,10 @@ int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
 #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))
 
+#define REXMIT_NONE	0 /* no loss recovery to do */
+#define REXMIT_LOST	1 /* retransmit packets marked lost */
+#define REXMIT_NEW	2 /* FRTO-style transmit of unsent/new packets */
+
 /* Adapt the MSS value used to make delayed ack decision to the
  * real world.
  */
@@ -1210,6 +1214,7 @@ static u8 tcp_sacktag_one(struct sock *sk,
 		sacked |= TCPCB_SACKED_ACKED;
 		state->flag |= FLAG_DATA_SACKED;
 		tp->sacked_out += pcount;
+		tp->delivered += pcount;  /* Out-of-order packets delivered */
 
 		fack_count += pcount;
 
@@ -1821,8 +1826,12 @@ static void tcp_check_reno_reordering(struct sock *sk, const int addend)
 static void tcp_add_reno_sack(struct sock *sk)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
+	u32 prior_sacked = tp->sacked_out;
+
 	tp->sacked_out++;
 	tcp_check_reno_reordering(sk, 0);
+	if (tp->sacked_out > prior_sacked)
+		tp->delivered++; /* Some out-of-order packet is delivered */
 	tcp_verify_left_out(tp);
 }
 
@@ -1834,6 +1843,7 @@ static void tcp_remove_reno_sacks(struct sock *sk, int acked)
 
 	if (acked > 0) {
 		/* One ACK acked hole. The rest eat duplicate ACKs. */
+		tp->delivered += max_t(int, acked - tp->sacked_out, 1);
 		if (acked - 1 >= tp->sacked_out)
 			tp->sacked_out = 0;
 		else
@@ -2467,14 +2477,12 @@ static void tcp_init_cwnd_reduction(struct sock *sk)
 	tcp_ecn_queue_cwr(tp);
 }
 
-static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
-			       int fast_rexmit, int flag)
+static void tcp_cwnd_reduction(struct sock *sk, int newly_acked_sacked,
+			       int flag)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	int sndcnt = 0;
 	int delta = tp->snd_ssthresh - tcp_packets_in_flight(tp);
-	int newly_acked_sacked = prior_unsacked -
-				 (tp->packets_out - tp->sacked_out);
 
 	if (newly_acked_sacked <= 0 || WARN_ON_ONCE(!tp->prior_cwnd))
 		return;
@@ -2492,7 +2500,8 @@ static void tcp_cwnd_reduction(struct sock *sk, const int prior_unsacked,
 	} else {
 		sndcnt = min(delta, newly_acked_sacked);
 	}
-	sndcnt = max(sndcnt, (fast_rexmit ? 1 : 0));
+	/* Force a fast retransmit upon entering fast recovery */
+	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
 	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
 }
 
@@ -2537,7 +2546,7 @@ static void tcp_try_keep_open(struct sock *sk)
 	}
 }
 
-static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
+static void tcp_try_to_open(struct sock *sk, int flag)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2551,8 +2560,6 @@ static void tcp_try_to_open(struct sock *sk, int flag, const int prior_unsacked)
 
 	if (inet_csk(sk)->icsk_ca_state != TCP_CA_CWR) {
 		tcp_try_keep_open(sk);
-	} else {
-		tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
 	}
 }
 
@@ -2662,7 +2669,8 @@ 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, bool is_dupack)
+static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack,
+			     int *rexmit)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	bool recovered = !before(tp->snd_una, tp->high_seq);
@@ -2684,10 +2692,15 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
 				tp->frto = 0; /* Step 3.a. loss was real */
 		} 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 */
+			/* Step 2.b. Try send new data (but deferred until cwnd
+			 * is updated in tcp_ack()). Otherwise fall back to
+			 * the conventional recovery.
+			 */
+			if (tcp_send_head(sk) &&
+			    after(tcp_wnd_end(tp), tp->snd_nxt)) {
+				*rexmit = REXMIT_NEW;
+				return;
+			}
 			tp->frto = 0;
 		}
 	}
@@ -2706,12 +2719,11 @@ static void tcp_process_loss(struct sock *sk, int flag, bool is_dupack)
 		else if (flag & FLAG_SND_UNA_ADVANCED)
 			tcp_reset_reno_sack(tp);
 	}
-	tcp_xmit_retransmit_queue(sk);
+	*rexmit = REXMIT_LOST;
 }
 
 /* Undo during fast recovery after partial ACK. */
-static bool tcp_try_undo_partial(struct sock *sk, const int acked,
-				 const int prior_unsacked, int flag)
+static bool tcp_try_undo_partial(struct sock *sk, const int acked)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -2726,10 +2738,8 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked,
 		 * can undo. Otherwise we clock out new packets but do not
 		 * mark more packets lost or retransmit more.
 		 */
-		if (tp->retrans_out) {
-			tcp_cwnd_reduction(sk, prior_unsacked, 0, flag);
+		if (tp->retrans_out)
 			return true;
-		}
 
 		if (!tcp_any_retrans_done(sk))
 			tp->retrans_stamp = 0;
@@ -2748,21 +2758,21 @@ static bool tcp_try_undo_partial(struct sock *sk, const int acked,
  * taking into account both packets sitting in receiver's buffer and
  * packets lost by network.
  *
- * Besides that it does CWND reduction, when packet loss is detected
- * and changes state of machine.
+ * Besides that it updates the congestion state when packet loss or ECN
+ * is detected. But it does not reduce the cwnd, it is done by the
+ * congestion control later.
  *
  * It does _not_ decide what to send, it is made in function
  * tcp_xmit_retransmit_queue().
  */
 static void tcp_fastretrans_alert(struct sock *sk, const int acked,
-				  const int prior_unsacked,
-				  bool is_dupack, int flag)
+				  bool is_dupack, int *ack_flag, int *rexmit)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
+	int fast_rexmit = 0, flag = *ack_flag;
 	bool do_lost = is_dupack || ((flag & FLAG_DATA_SACKED) &&
 				    (tcp_fackets_out(tp) > tp->reordering));
-	int fast_rexmit = 0;
 
 	if (WARN_ON(!tp->packets_out && tp->sacked_out))
 		tp->sacked_out = 0;
@@ -2809,8 +2819,10 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 
 	/* Use RACK to detect loss */
 	if (sysctl_tcp_recovery & TCP_RACK_LOST_RETRANS &&
-	    tcp_rack_mark_lost(sk))
+	    tcp_rack_mark_lost(sk)) {
 		flag |= FLAG_LOST_RETRANS;
+		*ack_flag |= FLAG_LOST_RETRANS;
+	}
 
 	/* E. Process state. */
 	switch (icsk->icsk_ca_state) {
@@ -2819,7 +2831,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 			if (tcp_is_reno(tp) && is_dupack)
 				tcp_add_reno_sack(sk);
 		} else {
-			if (tcp_try_undo_partial(sk, acked, prior_unsacked, flag))
+			if (tcp_try_undo_partial(sk, acked))
 				return;
 			/* Partial ACK arrived. Force fast retransmit. */
 			do_lost = tcp_is_reno(tp) ||
@@ -2831,7 +2843,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 		}
 		break;
 	case TCP_CA_Loss:
-		tcp_process_loss(sk, flag, is_dupack);
+		tcp_process_loss(sk, flag, is_dupack, rexmit);
 		if (icsk->icsk_ca_state != TCP_CA_Open &&
 		    !(flag & FLAG_LOST_RETRANS))
 			return;
@@ -2848,7 +2860,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 			tcp_try_undo_dsack(sk);
 
 		if (!tcp_time_to_recover(sk, flag)) {
-			tcp_try_to_open(sk, flag, prior_unsacked);
+			tcp_try_to_open(sk, flag);
 			return;
 		}
 
@@ -2870,8 +2882,7 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
 
 	if (do_lost)
 		tcp_update_scoreboard(sk, fast_rexmit);
-	tcp_cwnd_reduction(sk, prior_unsacked, fast_rexmit, flag);
-	tcp_xmit_retransmit_queue(sk);
+	*rexmit = REXMIT_LOST;
 }
 
 /* Kathleen Nichols' algorithm for tracking the minimum value of
@@ -3093,7 +3104,7 @@ static void tcp_ack_tstamp(struct sock *sk, struct sk_buff *skb,
  * arrived at the other end.
  */
 static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
-			       u32 prior_snd_una,
+			       u32 prior_snd_una, int *acked,
 			       struct tcp_sacktag_state *sack)
 {
 	const struct inet_connection_sock *icsk = inet_csk(sk);
@@ -3151,10 +3162,13 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 				flag |= FLAG_ORIG_SACK_ACKED;
 		}
 
-		if (sacked & TCPCB_SACKED_ACKED)
+		if (sacked & TCPCB_SACKED_ACKED) {
 			tp->sacked_out -= acked_pcount;
-		else if (tcp_is_sack(tp) && !tcp_skb_spurious_retrans(tp, skb))
-			tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
+		} else if (tcp_is_sack(tp)) {
+			tp->delivered += acked_pcount;
+			if (!tcp_skb_spurious_retrans(tp, skb))
+				tcp_rack_advance(tp, &skb->skb_mstamp, sacked);
+		}
 		if (sacked & TCPCB_LOST)
 			tp->lost_out -= acked_pcount;
 
@@ -3263,6 +3277,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 		}
 	}
 #endif
+	*acked = pkts_acked;
 	return flag;
 }
 
@@ -3296,9 +3311,6 @@ static inline bool tcp_ack_is_dubious(const struct sock *sk, const int flag)
 /* Decide wheather to run the increase function of congestion control. */
 static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 {
-	if (tcp_in_cwnd_reduction(sk))
-		return false;
-
 	/* If reordering is high then always grow cwnd whenever data is
 	 * delivered regardless of its ordering. Otherwise stay conservative
 	 * and only grow cwnd on in-order delivery (RFC5681). A stretched ACK w/
@@ -3311,6 +3323,24 @@ static inline bool tcp_may_raise_cwnd(const struct sock *sk, const int flag)
 	return flag & FLAG_DATA_ACKED;
 }
 
+/* The "ultimate" congestion control function that aims to replace the rigid
+ * cwnd increase and decrease control (tcp_cong_avoid,tcp_*cwnd_reduction).
+ * It's called toward the end of processing an ACK with precise rate
+ * information. All transmission or retransmission are delayed afterwards.
+ */
+static void tcp_cong_control(struct sock *sk, u32 ack, u32 acked_sacked,
+			     int flag)
+{
+	if (tcp_in_cwnd_reduction(sk)) {
+		/* Reduce cwnd if state mandates */
+		tcp_cwnd_reduction(sk, acked_sacked, flag);
+	} else if (tcp_may_raise_cwnd(sk, flag)) {
+		/* Advance cwnd if state allows */
+		tcp_cong_avoid(sk, ack, acked_sacked);
+	}
+	tcp_update_pacing_rate(sk);
+}
+
 /* Check that window update is acceptable.
  * The function assumes that snd_una<=ack<=snd_next.
  */
@@ -3506,6 +3536,27 @@ static inline void tcp_in_ack_event(struct sock *sk, u32 flags)
 		icsk->icsk_ca_ops->in_ack_event(sk, flags);
 }
 
+/* Congestion control has updated the cwnd already. So if we're in
+ * loss recovery then now we do any new sends (for FRTO) or
+ * retransmits (for CA_Loss or CA_recovery) that make sense.
+ */
+static void tcp_xmit_recovery(struct sock *sk, int rexmit)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (rexmit == REXMIT_NONE)
+		return;
+
+	if (unlikely(rexmit == 2)) {
+		__tcp_push_pending_frames(sk, tcp_current_mss(sk),
+					  TCP_NAGLE_OFF);
+		if (after(tp->snd_nxt, tp->high_seq))
+			return;
+		tp->frto = 0;
+	}
+	tcp_xmit_retransmit_queue(sk);
+}
+
 /* This routine deals with incoming acks, but not outgoing ones. */
 static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 {
@@ -3518,8 +3569,9 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	bool is_dupack = false;
 	u32 prior_fackets;
 	int prior_packets = tp->packets_out;
-	const int prior_unsacked = tp->packets_out - tp->sacked_out;
+	u32 prior_delivered = tp->delivered;
 	int acked = 0; /* Number of packets newly acked */
+	int rexmit = REXMIT_NONE; /* Flag to (re)transmit to recover losses */
 
 	sack_state.first_sackt.v64 = 0;
 
@@ -3608,23 +3660,16 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 		goto no_queue;
 
 	/* See if we can take anything off of the retransmit queue. */
-	acked = tp->packets_out;
-	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una,
+	flag |= tcp_clean_rtx_queue(sk, prior_fackets, prior_snd_una, &acked,
 				    &sack_state);
-	acked -= tp->packets_out;
 
 	if (tcp_ack_is_dubious(sk, flag)) {
 		is_dupack = !(flag & (FLAG_SND_UNA_ADVANCED | FLAG_NOT_DUP));
-		tcp_fastretrans_alert(sk, acked, prior_unsacked,
-				      is_dupack, flag);
+		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
 	}
 	if (tp->tlp_high_seq)
 		tcp_process_tlp_ack(sk, ack, flag);
 
-	/* Advance cwnd if state allows */
-	if (tcp_may_raise_cwnd(sk, flag))
-		tcp_cong_avoid(sk, ack, acked);
-
 	if ((flag & FLAG_FORWARD_PROGRESS) || !(flag & FLAG_NOT_DUP)) {
 		struct dst_entry *dst = __sk_dst_get(sk);
 		if (dst)
@@ -3633,14 +3678,14 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
 	if (icsk->icsk_pending == ICSK_TIME_RETRANS)
 		tcp_schedule_loss_probe(sk);
-	tcp_update_pacing_rate(sk);
+	tcp_cong_control(sk, ack, tp->delivered - prior_delivered, flag);
+	tcp_xmit_recovery(sk, rexmit);
 	return 1;
 
 no_queue:
 	/* If data was DSACKed, see if we can undo a cwnd reduction. */
 	if (flag & FLAG_DSACKING_ACK)
-		tcp_fastretrans_alert(sk, acked, prior_unsacked,
-				      is_dupack, flag);
+		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
 	/* If this ack opens up a zero window, clear backoff.  It was
 	 * being used to time the probes, and is probably far higher than
 	 * it needs to be for normal retransmission.
@@ -3663,8 +3708,8 @@ old_ack:
 	if (TCP_SKB_CB(skb)->sacked) {
 		flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
 						&sack_state);
-		tcp_fastretrans_alert(sk, acked, prior_unsacked,
-				      is_dupack, flag);
+		tcp_fastretrans_alert(sk, acked, is_dupack, &flag, &rexmit);
+		tcp_xmit_recovery(sk, rexmit);
 	}
 
 	SOCK_DEBUG(sk, "Ack %u before %u:%u\n", ack, tp->snd_una, tp->snd_nxt);