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authorEric Dumazet <edumazet@google.com>2013-08-05 20:05:12 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2013-09-14 05:50:47 -0700
commitdd3004635fe0607f64ca9ceca51f209fbc0a09a6 (patch)
parent28e9a84cdf505686ac00ead1adcbc75f26b48487 (diff)
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index b9d22e62074b..b78eac2b7079 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)
/* 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)
delay = (rtt_us << 3) / USEC_PER_MSEC;