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Commit 49ff4bb4 authored by Ilpo Järvinen's avatar Ilpo Järvinen Committed by David S. Miller
Browse files

[TCP]: DSACK signals data receival, be conservative 



In case a DSACK is received, it's better to lower cwnd as it's
a sign of data receival.

Signed-off-by: default avatarIlpo Järvinen <ilpo.jarvinen@helsinki.fi>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2e605294

net/ipv4/tcp_input.c

+4 −1
Original line number Diff line number Diff line
@@ -103,6 +103,7 @@ int sysctl_tcp_abc __read_mostly; 
#define FLAG_SLOWPATH		0x100 /* Do not skip RFC checks for window update.*/

#define FLAG_ONLY_ORIG_SACKED	0x200 /* SACKs only non-rexmit sent before RTO */

#define FLAG_SND_UNA_ADVANCED	0x400 /* Snd_una was changed (!= FLAG_DATA_ACKED) */

#define FLAG_DSACKING_ACK	0x800 /* SACK blocks contained DSACK info */



#define FLAG_ACKED		(FLAG_DATA_ACKED|FLAG_SYN_ACKED)

#define FLAG_NOT_DUP		(FLAG_DATA|FLAG_WIN_UPDATE|FLAG_ACKED)
@@ -966,12 +967,14 @@ tcp_sacktag_write_queue(struct sock *sk, struct sk_buff *ack_skb, u32 prior_snd_ 


	/* Check for D-SACK. */

	if (before(ntohl(sp[0].start_seq), TCP_SKB_CB(ack_skb)->ack_seq)) {

		flag |= FLAG_DSACKING_ACK;

		found_dup_sack = 1;

		tp->rx_opt.sack_ok |= 4;

		NET_INC_STATS_BH(LINUX_MIB_TCPDSACKRECV);

	} else if (num_sacks > 1 &&

			!after(ntohl(sp[0].end_seq), ntohl(sp[1].end_seq)) &&

			!before(ntohl(sp[0].start_seq), ntohl(sp[1].start_seq))) {

		flag |= FLAG_DSACKING_ACK;

		found_dup_sack = 1;

		tp->rx_opt.sack_ok |= 4;

		NET_INC_STATS_BH(LINUX_MIB_TCPDSACKOFORECV);
@@ -1858,7 +1861,7 @@ static void tcp_cwnd_down(struct sock *sk, int flag) 
	struct tcp_sock *tp = tcp_sk(sk);

	int decr = tp->snd_cwnd_cnt + 1;



	if ((flag&FLAG_ANY_PROGRESS) ||

	if ((flag&(FLAG_ANY_PROGRESS|FLAG_DSACKING_ACK)) ||

	    (IsReno(tp) && !(flag&FLAG_NOT_DUP))) {

		tp->snd_cwnd_cnt = decr&1;

		decr >>= 1;