From: Ilpo Järvinen commit 49ff4bb4cd4c04acf8f9e3d3ec2148305a1db445 in mainline. [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: Ilpo Järvinen Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/tcp_input.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -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, /* 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 *s 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; -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/