| From | Luis Henriques <> | Subject | [PATCH 044/104] tcp: cubic: fix bug in bictcp_acked() | Date | Mon, 30 Sep 2013 11:10:21 +0100 |
| |
3.5.7.22 -stable review patch. If anyone has any objections, please let me know.
------------------
From: Eric Dumazet <edumazet@google.com>
commit cd6b423afd3c08b27e1fed52db828ade0addbc6b upstream.
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@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Neal Cardwell <ncardwell@google.com> Cc: Yuchung Cheng <ycheng@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- net/ipv4/tcp_cubic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index b6b591f..b6ae92a 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -416,7 +416,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) 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; -- 1.8.3.2
|