From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: ncardwell@google.com, netdev@vger.kernel.org, vanj@google.com,
ycheng@google.com
Subject: Re: [PATCH] tcp: cubic: fix bug in bictcp_acked()
Date: Wed, 07 Aug 2013 10:37:02 -0700 (PDT) [thread overview]
Message-ID: <20130807.103702.2279717727976902224.davem@davemloft.net> (raw)
In-Reply-To: <1375758312.4457.69.camel@edumazet-glaptop>
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.
prev parent reply other threads:[~2013-08-07 17:31 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-06 3:05 [PATCH] tcp: cubic: fix bug in bictcp_acked() Eric Dumazet
2013-08-06 13:49 ` Neal Cardwell
2013-08-07 17:37 ` David Miller [this message]
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