This is a note to let you know that I've just added the patch titled
tcp: avoid cwnd moderation in undo
to the 2.6.38-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
tcp-avoid-cwnd-moderation-in-undo.patch
and it can be found in the queue-2.6.38 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <[email protected]> know about it.
>From bd59e4b2b325a4f0fcd491a8ec55a619fef91ded Mon Sep 17 00:00:00 2001
From: Yuchung Cheng <[email protected]>
Date: Mon, 14 Mar 2011 10:57:03 +0000
Subject: tcp: avoid cwnd moderation in undo
From: Yuchung Cheng <[email protected]>
[ Upstream commit 67d4120a1793138bc9f4a6eb61d0fc5298ed97e0 ]
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 <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
net/ipv4/tcp_input.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2659,7 +2659,7 @@ static void DBGUNDO(struct sock *sk, con
#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
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
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);
}
Patches currently in stable-queue which might be from [email protected] are
queue-2.6.38/tcp-avoid-cwnd-moderation-in-undo.patch
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