path: root/net/ipv4
diff options
authorAki M Nyrhinen <anyrhine@cs.helsinki.fi>2006-06-11 21:18:56 -0700
committerDavid S. Miller <davem@davemloft.net>2006-06-11 21:18:56 -0700
commit79320d7e14900c549c3520791a297328f53ff71e (patch)
treebd2c9cc7f2d4b7790ad1e18fb9a00aad621c0354 /net/ipv4
parent[DCCP] Ackvec: fix soft lockup in ackvec handling code (diff)
[TCP]: continued: reno sacked_out count fix
From: Aki M Nyrhinen <anyrhine@cs.helsinki.fi> IMHO the current fix to the problem (in_flight underflow in reno) is incorrect. it treats the symptons but ignores the problem. the problem is timing out packets other than the head packet when we don't have sack. i try to explain (sorry if explaining the obvious). with sack, scanning the retransmit queue for timed out packets is fine because we know which packets in our retransmit queue have been acked by the receiver. without sack, we know only how many packets in our retransmit queue the receiver has acknowledged, but no idea which packets. think of a "typical" slow-start overshoot case, where for example every third packet in a window get lost because a router buffer gets full. with sack, we check for timeouts on those every third packet (as the rest have been sacked). the packet counting works out and if there is no reordering, we'll retransmit exactly the packets that were lost. without sack, however, we check for timeout on every packet and end up retransmitting consecutive packets in the retransmit queue. in our slow-start example, 2/3 of those retransmissions are unnecessary. these unnecessary retransmissions eat the congestion window and evetually prevent fast recovery from continuing, if enough packets were lost. Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4')
1 files changed, 1 insertions, 3 deletions
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 4a538bc1683d..b5521a9d3dc1 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1649,7 +1649,7 @@ static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
* Hence, we can detect timed out packets during fast
* retransmit without falling to slow start.
- if (tcp_head_timedout(sk, tp)) {
+ if (!IsReno(tp) && tcp_head_timedout(sk, tp)) {
struct sk_buff *skb;
skb = tp->scoreboard_skb_hint ? tp->scoreboard_skb_hint
@@ -1662,8 +1662,6 @@ static void tcp_update_scoreboard(struct sock *sk, struct tcp_sock *tp)
if (!(TCP_SKB_CB(skb)->sacked&TCPCB_TAGBITS)) {
TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
tp->lost_out += tcp_skb_pcount(skb);
- if (IsReno(tp))
- tcp_remove_reno_sacks(sk, tp, tcp_skb_pcount(skb) + 1);
/* clear xmit_retrans hint */
if (tp->retransmit_skb_hint &&