This is a note to let you know that I've just added the patch titled
tcp: cubic: fix bug in bictcp_acked()
to the 3.0-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-cubic-fix-bug-in-bictcp_acked.patch
and it can be found in the queue-3.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 72af21fc42ef8882ffa2feba3712117b178707c0 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@xxxxxxxxxx>
Date: Mon, 5 Aug 2013 20:05:12 -0700
Subject: tcp: cubic: fix bug in bictcp_acked()
From: Eric Dumazet <edumazet@xxxxxxxxxx>
[ Upstream commit cd6b423afd3c08b27e1fed52db828ade0addbc6b ]
While investigating about strange increase of retransmit rates
on hosts ~24 days after boot, Van found hystart was disabled
if ca->epoch_start was 0, as following condition is true
when tcp_time_stamp high order bit is set.
(s32)(tcp_time_stamp - ca->epoch_start) < HZ
Quoting Van :
At initialization & after every loss ca->epoch_start is set to zero so
I believe that the above line will turn off hystart as soon as the 2^31
bit is set in tcp_time_stamp & hystart will stay off for 24 days.
I think we've observed that cubic's restart is too aggressive without
hystart so this might account for the higher drop rate we observe.
Diagnosed-by: Van Jacobson <vanj@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
Cc: Yuchung Cheng <ycheng@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp_cubic.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -414,7 +414,7 @@ static void bictcp_acked(struct sock *sk
return;
/* Discard delay samples right after fast recovery */
- if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ)
+ if (ca->epoch_start && (s32)(tcp_time_stamp - ca->epoch_start) < HZ)
return;
delay = (rtt_us << 3) / USEC_PER_MSEC;
Patches currently in stable-queue which might be from edumazet@xxxxxxxxxx are
queue-3.0/fib_trie-remove-potential-out-of-bound-access.patch
queue-3.0/net-check-net.core.somaxconn-sysctl-values.patch
queue-3.0/tcp-cubic-fix-bug-in-bictcp_acked.patch
queue-3.0/tcp-cubic-fix-overflow-error-in-bictcp_update.patch
queue-3.0/htb-fix-sign-extension-bug.patch
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