Commit 3d0d26c7 authored Apr 11, 2015 by Kenneth Klette Jonassen Committed by David S. Miller Apr 13, 2015

tcp: fix bogus RTT for CC when retransmissions are acked

Since retransmitted segments are not used for RTT estimation, previously
SACKed segments present in the rtx queue are used. This estimation can be
several times larger than the actual RTT. When a cumulative ack covers both
previously SACKed and retransmitted segments, CC may thus get a bogus RTT.

Such segments previously had an RTT estimation in tcp_sacktag_one(), so it
seems reasonable to not reuse them in tcp_clean_rtx_queue() at all.

Afaik, this has had no effect on SRTT/RTO because of Karn's check.

Signed-off-by: Kenneth Klette Jonassen <kennetkl@ifi.uio.no>
Acked-by: Neal Cardwell <ncardwell@google.com>
Tested-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 4577139b

net/ipv4/tcp_input.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -3099,18 +3099,16 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
		if (sacked & TCPCB_SACKED_RETRANS)
		tp->retrans_out -= acked_pcount;
		flag \|= FLAG_RETRANS_DATA_ACKED;
		} else {
		} else if (!(sacked & TCPCB_SACKED_ACKED)) {
		last_ackt = skb->skb_mstamp;
		WARN_ON_ONCE(last_ackt.v64 == 0);
		if (!first_ackt.v64)
		first_ackt = last_ackt;

		if (!(sacked & TCPCB_SACKED_ACKED)) {
		reord = min(pkts_acked, reord);
		if (!after(scb->end_seq, tp->high_seq))
		flag \|= FLAG_ORIG_SACK_ACKED;
		}
		}

		if (sacked & TCPCB_SACKED_ACKED)
		tp->sacked_out -= acked_pcount;

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