tcp: ensure to use the most recently sent skb when filling the rate sample

If an ACK (s)acks multiple skbs, we favor the information
from the most recently sent skb by choosing the skb with
the highest prior_delivered count. But in the interval
between receiving ACKs, we send multiple skbs with the same
prior_delivered, because the tp->delivered only changes
when we receive an ACK.

We used RACK's solution, copying tcp_rack_sent_after() as
tcp_skb_sent_after() helper to determine "which packet was
sent last?". Later, we will use tcp_skb_sent_after() instead
in RACK.

Fixes: b9f64820fb22 ("tcp: track data delivery rate for a TCP connection")
Signed-off-by: Pengcheng Yang <yangpc@wangsu.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Tested-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/r/1650422081-22153-1-git-send-email-yangpc@wangsu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 8 insertions, 3 deletions

diff --git a/net/ipv4/tcp_rate.c b/net/ipv4/tcp_rate.c
index fbab921670cc..9a8e014d9b5b 100644
--- a/net/ipv4/tcp_rate.c
+++ b/net/ipv4/tcp_rate.c
@@ -74,27 +74,32 @@ void tcp_rate_skb_sent(struct sock *sk, struct sk_buff *skb)
  *
  * If an ACK (s)acks multiple skbs (e.g., stretched-acks), this function is
  * called multiple times. We favor the information from the most recently
- * sent skb, i.e., the skb with the highest prior_delivered count.
+ * sent skb, i.e., the skb with the most recently sent time and the highest
+ * sequence.
  */
 void tcp_rate_skb_delivered(struct sock *sk, struct sk_buff *skb,
 			    struct rate_sample *rs)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct tcp_skb_cb *scb = TCP_SKB_CB(skb);
+	u64 tx_tstamp;
 
 	if (!scb->tx.delivered_mstamp)
 		return;
 
+	tx_tstamp = tcp_skb_timestamp_us(skb);
 	if (!rs->prior_delivered ||
-	    after(scb->tx.delivered, rs->prior_delivered)) {
+	    tcp_skb_sent_after(tx_tstamp, tp->first_tx_mstamp,
+			       scb->end_seq, rs->last_end_seq)) {
 		rs->prior_delivered_ce  = scb->tx.delivered_ce;
 		rs->prior_delivered  = scb->tx.delivered;
 		rs->prior_mstamp     = scb->tx.delivered_mstamp;
 		rs->is_app_limited   = scb->tx.is_app_limited;
 		rs->is_retrans	     = scb->sacked & TCPCB_RETRANS;
+		rs->last_end_seq     = scb->end_seq;
 
 		/* Record send time of most recently ACKed packet: */
-		tp->first_tx_mstamp  = tcp_skb_timestamp_us(skb);
+		tp->first_tx_mstamp  = tx_tstamp;
 		/* Find the duration of the "send phase" of this window: */
 		rs->interval_us = tcp_stamp_us_delta(tp->first_tx_mstamp,
 						     scb->tx.first_tx_mstamp);