net-tcp_bbr: v2: count packets lost over TCP rate sampling interval

For understanding the relationship between inflight and packet loss
signals, to try to find the highest inflight value that has acceptable
levels of packet losses.

Effort: net-tcp_bbr
Origin-9xx-SHA1: 4527e26b2bd7756a88b5b9ef1ada3da33dd609ab
Change-Id: I594c2500868d9c530770e7ddd68ffc87c57f4fd5

include/net/tcp.h

@@ -886,6 +886,7 @@ struct tcp_skb_cb {
 #define TCPCB_IN_FLIGHT_MAX ((1U << TCPCB_IN_FLIGHT_BITS) - 1)
 			u32 in_flight:20,   /* packets in flight at transmit */
 			    unused2:12;
+			u32 lost;	/* packets lost so far upon tx of skb */
 		} tx;   /* only used for outgoing skbs */
 		union {
 			struct inet_skb_parm	h4;
@@ -1055,11 +1056,13 @@ struct ack_sample {
  */
 struct rate_sample {
 	u64  prior_mstamp; /* starting timestamp for interval */
+	u32  prior_lost;	/* tp->lost at "prior_mstamp" */
 	u32  prior_delivered;	/* tp->delivered at "prior_mstamp" */
 	u32  prior_delivered_ce;/* tp->delivered_ce at "prior_mstamp" */
 	u32 tx_in_flight;	/* packets in flight at starting timestamp */
+	s32  lost;		/* number of packets lost over interval */
 	s32  delivered;		/* number of packets delivered over interval */
-	s32  delivered_ce;	/* number of packets delivered w/ CE marks*/
+	s32  delivered_ce;	/* packets delivered w/ CE mark over interval */
 	long interval_us;	/* time for tp->delivered to incr "delivered" */
 	u32 snd_interval_us;	/* snd interval for delivered packets */
 	u32 rcv_interval_us;	/* rcv interval for delivered packets */

net/ipv4/tcp_rate.c

@@ -67,6 +67,7 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
 	TCP_SKB_CB(skb)->tx.delivered_mstamp	= tp->delivered_mstamp;
 	TCP_SKB_CB(skb)->tx.delivered		= tp->delivered;
 	TCP_SKB_CB(skb)->tx.delivered_ce	= tp->delivered_ce;
+	TCP_SKB_CB(skb)->tx.lost		= tp->lost;
 	TCP_SKB_CB(skb)->tx.is_app_limited	= tp->app_limited ? 1 : 0;
 
 	/* Check, sanitize, and record packets in flight after skb was sent. */
@@ -100,6 +101,7 @@ void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 
 	if (!rs->prior_delivered ||
 	    after(scb->tx.delivered, rs->prior_delivered)) {
+		rs->prior_lost	     = scb->tx.lost;
 		rs->prior_delivered_ce  = scb->tx.delivered_ce;
 		rs->prior_delivered  = scb->tx.delivered;
 		rs->prior_mstamp     = scb->tx.delivered_mstamp;
@@ -154,6 +156,7 @@ void tcp_rate_gen(struct sock *sk, u32 delivered, u32 lost,
 		return;
 	}
 	rs->delivered   = tp->delivered - rs->prior_delivered;
+	rs->lost        = tp->lost - rs->prior_lost;
 
 	rs->delivered_ce = tp->delivered_ce - rs->prior_delivered_ce;
 	/* delivered_ce occupies less than 32 bits in the skb control block */