From: David Miller <davem@davemloft.net>
To: eric.dumazet@gmail.com
Cc: netdev@vger.kernel.org, ncardwell@google.com, ycheng@google.com,
jri@google.com
Subject: Re: [PATCH net] tcp_cubic: do not set epoch_start in the future
Date: Thu, 17 Sep 2015 22:35:35 -0700 (PDT) [thread overview]
Message-ID: <20150917.223535.157337200633800999.davem@davemloft.net> (raw)
In-Reply-To: <1442504280.16225.15.camel@edumazet-glaptop2.roam.corp.google.com>
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 17 Sep 2015 08:38:00 -0700
> From: Eric Dumazet <edumazet@google.com>
>
> Tracking idle time in bictcp_cwnd_event() is imprecise, as epoch_start
> is normally set at ACK processing time, not at send time.
>
> Doing a proper fix would need to add an additional state variable,
> and does not seem worth the trouble, given CUBIC bug has been there
> forever before Jana noticed it.
>
> Let's simply not set epoch_start in the future, otherwise
> bictcp_update() could overflow and CUBIC would again
> grow cwnd too fast.
>
> This was detected thanks to a packetdrill test Neal wrote that was flaky
> before applying this fix.
>
> Fixes: 30927520dbae ("tcp_cubic: better follow cubic curve after idle period")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Cc: Jana Iyengar <jri@google.com>
Applied, thanks.
prev parent reply other threads:[~2015-09-18 5:35 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-17 15:38 [PATCH net] tcp_cubic: do not set epoch_start in the future Eric Dumazet
2015-09-18 5:35 ` David Miller [this message]
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