| From: Eric Dumazet <edumazet@google.com> |
| Date: Mon, 5 Aug 2013 20:05:12 -0700 |
| Subject: tcp: cubic: fix bug in bictcp_acked() |
| |
| [ 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@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: Ben Hutchings <ben@decadent.org.uk> |
| --- |
| 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 b9d22e6..b78eac2 100644 |
| --- a/net/ipv4/tcp_cubic.c |
| +++ b/net/ipv4/tcp_cubic.c |
| @@ -414,7 +414,7 @@ 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; |
