| Message ID | 1375758312.4457.69.camel@edumazet-glaptop |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Mon, Aug 5, 2013 at 11:05 PM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > From: Eric Dumazet <edumazet@google.com> > > 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> Nice catch! neal -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Mon, 05 Aug 2013 20:05:12 -0700 > From: Eric Dumazet <edumazet@google.com> > > 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> Applied and queued up for -stable, thanks. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index a9077f4..2b8671d 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;