[46/50] Fix TCP DSACK cwnd handling

Greg KH
2007-09-24T16:42:52Z

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: fix-tcp-dsack-cwnd-handling.patch --]
[-- Type: text/plain; charset=unknown-8bit, Size: 1930 bytes --]

From: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>

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 <ilpo.jarvinen@helsinki.fi>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
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;

--