From 67d4120a1793138bc9f4a6eb61d0fc5298ed97e0 Mon Sep 17 00:00:00 2001
From: Yuchung Cheng <ycheng@google.com>
Date: Mon, 14 Mar 2011 10:57:03 +0000
Subject: tcp: avoid cwnd moderation in undo
In the current undo logic, cwnd is moderated after it was restored
to the value prior entering fast-recovery. It was moderated first
in tcp_try_undo_recovery then again in tcp_complete_cwr.
Since the undo indicates recovery was false, these moderations
are not necessary. If the undo is triggered when most of the
outstanding data have been acknowledged, the (restored) cwnd is
falsely pulled down to a small value.
This patch removes these cwnd moderations if cwnd is undone
a) during fast-recovery
b) by receiving DSACKs past fast-recovery
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/tcp_input.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
(limited to 'net/ipv4/tcp_input.c')
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index da782e7ab16d..e72af7e31d1c 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2659,7 +2659,7 @@ static void DBGUNDO(struct sock *sk, const char *msg)
#define DBGUNDO(x...) do { } while (0)
#endif
-static void tcp_undo_cwr(struct sock *sk, const int undo)
+static void tcp_undo_cwr(struct sock *sk, const int undo_ssthresh)
{
struct tcp_sock *tp = tcp_sk(sk);
@@ -2671,14 +2671,13 @@ static void tcp_undo_cwr(struct sock *sk, const int undo)
else
tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh << 1);
- if (undo && tp->prior_ssthresh > tp->snd_ssthresh) {
+ if (undo_ssthresh && tp->prior_ssthresh > tp->snd_ssthresh) {
tp->snd_ssthresh = tp->prior_ssthresh;
TCP_ECN_withdraw_cwr(tp);
}
} else {
tp->snd_cwnd = max(tp->snd_cwnd, tp->snd_ssthresh);
}
- tcp_moderate_cwnd(tp);
tp->snd_cwnd_stamp = tcp_time_stamp;
}
@@ -2822,8 +2821,11 @@ static int tcp_try_undo_loss(struct sock *sk)
static inline void tcp_complete_cwr(struct sock *sk)
{
struct tcp_sock *tp = tcp_sk(sk);
- tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
- tp->snd_cwnd_stamp = tcp_time_stamp;
+ /* Do not moderate cwnd if it's already undone in cwr or recovery */
+ if (tp->undo_marker && tp->snd_cwnd > tp->snd_ssthresh) {
+ tp->snd_cwnd = tp->snd_ssthresh;
+ tp->snd_cwnd_stamp = tcp_time_stamp;
+ }
tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
}
--
cgit v1.2.3-70-g09d2
From f6152737a95bd6c22f0c664b20831aefd48085a8 Mon Sep 17 00:00:00 2001
From: "David S. Miller" <davem@davemloft.net>
Date: Tue, 22 Mar 2011 19:37:11 -0700
Subject: tcp: Make undo_ssthresh arg to tcp_undo_cwr() a bool.
Signed-off-by: David S. Miller <davem@davemloft.net>
---
net/ipv4/tcp_input.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
(limited to 'net/ipv4/tcp_input.c')
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index e72af7e31d1c..bef9f04c22ba 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2659,7 +2659,7 @@ static void DBGUNDO(struct sock *sk, const char *msg)
#define DBGUNDO(x...) do { } while (0)
#endif
-static void tcp_undo_cwr(struct sock *sk, const int undo_ssthresh)
+static void tcp_undo_cwr(struct sock *sk, const bool undo_ssthresh)
{
struct tcp_sock *tp = tcp_sk(sk);
@@ -2698,7 +2698,7 @@ static int tcp_try_undo_recovery(struct sock *sk)
* or our original transmission succeeded.
*/
DBGUNDO(sk, inet_csk(sk)->icsk_ca_state == TCP_CA_Loss ? "loss" : "retrans");
- tcp_undo_cwr(sk, 1);
+ tcp_undo_cwr(sk, true);
if (inet_csk(sk)->icsk_ca_state == TCP_CA_Loss)
mib_idx = LINUX_MIB_TCPLOSSUNDO;
else
@@ -2725,7 +2725,7 @@ static void tcp_try_undo_dsack(struct sock *sk)
if (tp->undo_marker && !tp->undo_retrans) {
DBGUNDO(sk, "D-SACK");
- tcp_undo_cwr(sk, 1);
+ tcp_undo_cwr(sk, true);
tp->undo_marker = 0;
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPDSACKUNDO);
}
@@ -2778,7 +2778,7 @@ static int tcp_try_undo_partial(struct sock *sk, int acked)
tcp_update_reordering(sk, tcp_fackets_out(tp) + acked, 1);
DBGUNDO(sk, "Hoe");
- tcp_undo_cwr(sk, 0);
+ tcp_undo_cwr(sk, false);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPPARTIALUNDO);
/* So... Do not make Hoe's retransmit yet.
@@ -2807,7 +2807,7 @@ static int tcp_try_undo_loss(struct sock *sk)
DBGUNDO(sk, "partial loss");
tp->lost_out = 0;
- tcp_undo_cwr(sk, 1);
+ tcp_undo_cwr(sk, true);
NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPLOSSUNDO);
inet_csk(sk)->icsk_retransmits = 0;
tp->undo_marker = 0;
@@ -3496,7 +3496,7 @@ static void tcp_undo_spur_to_response(struct sock *sk, int flag)
if (flag & FLAG_ECE)
tcp_ratehalving_spur_to_response(sk);
else
- tcp_undo_cwr(sk, 1);
+ tcp_undo_cwr(sk, true);
}
/* F-RTO spurious RTO detection algorithm (RFC4138)
--
cgit v1.2.3-70-g09d2