net-tcp_bbr: v2: introduce is_acking_tlp_retrans_seq into rate_sample

Introduce is_acking_tlp_retrans_seq into rate_sample. This bool will
export to the CC module the knowledge of whether the current ACK
matched a TLP retransmit.

Note that when this bool is true, we cannot yet tell (in general) whether
this ACK is for the original or the TLP retransmit.

Effort: net-tcp_bbr
Change-Id: I2e6494332167e75efcbdc99bd5c119034e9c39b4
Signed-off-by: Alexandre Frade <kernel@xanmod.org>

include/net/tcp.h

@@ -1079,6 +1079,7 @@ struct rate_sample {
 	u32  last_end_seq;	/* end_seq of most recently ACKed packet */
 	bool is_app_limited;	/* is sample from packet with bubble in pipe? */
 	bool is_retrans;	/* is sample from retransmission? */
+	bool is_acking_tlp_retrans_seq;  /* ACKed a TLP retransmit sequence? */
 	bool is_ack_delayed;	/* is this (likely) a delayed ACK? */
 	bool is_ece;		/* did this ACK have ECN marked? */
 };

net/ipv4/tcp_input.c

@@ -3703,7 +3703,8 @@ static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
 /* This routine deals with acks during a TLP episode and ends an episode by
  * resetting tlp_high_seq. Ref: TLP algorithm in draft-ietf-tcpm-rack
  */
-static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
+static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag,
+				struct rate_sample *rs)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 
@@ -3731,6 +3732,11 @@ static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
 			     FLAG_NOT_DUP | FLAG_DATA_SACKED))) {
 		/* Pure dupack: original and TLP probe arrived; no loss */
 		tp->tlp_high_seq = 0;
+	} else {
+		/* This ACK matches a TLP retransmit. We cannot yet tell if
+		 * this ACK is for the original or the TLP retransmit.
+		 */
+		rs->is_acking_tlp_retrans_seq = 1;
 	}
 }
 
@@ -3910,7 +3916,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	tcp_rack_update_reo_wnd(sk, &rs);
 
 	if (tp->tlp_high_seq)
-		tcp_process_tlp_ack(sk, ack, flag);
+		tcp_process_tlp_ack(sk, ack, flag, &rs);
 
 	if (tcp_ack_is_dubious(sk, flag)) {
 		if (!(flag & (FLAG_SND_UNA_ADVANCED |
@@ -3954,7 +3960,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 	tcp_ack_probe(sk);
 
 	if (tp->tlp_high_seq)
-		tcp_process_tlp_ack(sk, ack, flag);
+		tcp_process_tlp_ack(sk, ack, flag, &rs);
 	return 1;
 
 old_ack: