diff options
| author | Eric Dumazet <edumazet@google.com> | 2013-08-05 20:05:12 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2013-08-07 10:35:08 -0700 |
| commit | cd6b423afd3c08b27e1fed52db828ade0addbc6b (patch) | |
| tree | ca239e247313b1817f811a462c79184adb102d6e /net/ipv4/tcp_cubic.c | |
| parent | 15401946f9b720efdd20bda3ae79725e9c586897 (diff) | |
| download | lwn-cd6b423afd3c08b27e1fed52db828ade0addbc6b.tar.gz lwn-cd6b423afd3c08b27e1fed52db828ade0addbc6b.zip | |
tcp: cubic: fix bug in bictcp_acked()
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>
Diffstat (limited to 'net/ipv4/tcp_cubic.c')
| -rw-r--r-- | net/ipv4/tcp_cubic.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index b6b591f0a788..b6ae92a51f58 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; |