netdev - [PATCH net-next 2/2] tcp: TLP retransmits last if failed to send new packet

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Message-Id: <1437168172-24201-3-git-send-email-ycheng@google.com>
Date:	Fri, 17 Jul 2015 14:22:52 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	davem@...emloft.net
Cc:	netdev@...r.kernel.org, Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Nanditad Dukkipati <nanditad@...gle.com>
Subject: [PATCH net-next 2/2] tcp: TLP retransmits last if failed to send new packet

When TLP fails to send new packet because of receive window
limit or other reasons, it should fall back to retransmit
the last packet, instead of resorting to RTO.

Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
Signed-off-by: Nanditad Dukkipati <nanditad@...gle.com>
---
 net/ipv4/tcp_output.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index deb944b..4f238bb 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2226,7 +2226,7 @@ static bool skb_still_in_host_queue(const struct sock *sk,
 	return false;
 }
 
-/* When probe timeout (PTO) fires, send a new segment if one exists, else
+/* When probe timeout (PTO) fires, try send a new segment if possible, else
  * retransmit the last segment.
  */
 void tcp_send_loss_probe(struct sock *sk)
@@ -2237,9 +2237,14 @@ void tcp_send_loss_probe(struct sock *sk)
 	int mss = tcp_current_mss(sk);
 	int err = -1;
 
-	if (tcp_send_head(sk)) {
+	skb = tcp_send_head(sk);
+	if (skb) {
 		err = tcp_write_xmit(sk, mss, TCP_NAGLE_OFF, 2, GFP_ATOMIC);
-		goto rearm_timer;
+		if (!err)
+			goto rearm_timer;
+		skb = tcp_write_queue_prev(sk, skb);
+	} else {
+		skb = tcp_write_queue_tail(sk);
 	}
 
 	/* At most one outstanding TLP retransmission. */
@@ -2247,7 +2252,6 @@ void tcp_send_loss_probe(struct sock *sk)
 		goto rearm_timer;
 
 	/* Retransmit last segment. */
-	skb = tcp_write_queue_tail(sk);
 	if (WARN_ON(!skb))
 		goto rearm_timer;
 
@@ -2262,7 +2266,7 @@ void tcp_send_loss_probe(struct sock *sk)
 		if (unlikely(tcp_fragment(sk, skb, (pcount - 1) * mss, mss,
 					  GFP_ATOMIC)))
 			goto rearm_timer;
-		skb = tcp_write_queue_tail(sk);
+		skb = tcp_write_queue_next(sk, skb);
 	}
 
 	if (WARN_ON(!skb || !tcp_skb_pcount(skb)))
-- 
2.4.3.573.g4eafbef

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