netdev - [PATCH net-next] tcp: use SACK RTTs for CC

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Date:	Thu, 29 Jan 2015 20:08:03 +0100
From:	Kenneth Klette Jonassen <kennetkl@....uio.no>
To:	netdev@...r.kernel.org
Cc:	Kenneth Klette Jonassen <kennetkl@....uio.no>
Subject: [PATCH net-next] tcp: use SACK RTTs for CC

Current behavior only passes RTTs from sequentially acked data to CC.

If sender gets a combined ACK for segment 1 and SACK for segment 3, then the
computed RTT for CC is the time between sending segment 1 and receiving SACK
for segment 3.

Pass the minimum computed RTT from any acked data to CC, i.e. time between
sending segment 3 and receiving SACK for segment 3.

Signed-off-by: Kenneth Klette Jonassen <kennetkl@....uio.no>
---
 net/ipv4/tcp_input.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 71fb37c..ed11931 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3183,8 +3183,10 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
 
 		tp->fackets_out -= min(pkts_acked, tp->fackets_out);
 
-		if (ca_ops->pkts_acked)
-			ca_ops->pkts_acked(sk, pkts_acked, ca_seq_rtt_us);
+		if (ca_ops->pkts_acked) {
+			long rtt_us = min_t(ulong, ca_seq_rtt_us, sack_rtt_us);
+			ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
+		}
 
 	} else if (skb && rtt_update && sack_rtt_us >= 0 &&
 		   sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
-- 
1.9.1

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