3.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <eduma...@google.com>
[ 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 <v...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Cc: Neal Cardwell <ncardw...@google.com>
Cc: Yuchung Cheng <ych...@google.com>
Acked-by: Neal Cardwell <ncardw...@google.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
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
@@ -416,7 +416,7 @@ 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;
--
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