From: Stephen Hemminger <stephen@networkplumber.org>
To: Yuchung Cheng <ycheng@google.com>
Cc: davem@davemloft.net, netdev@vger.kernel.org,
ncardwell@google.com, edumazet@google.com, soheil@google.com
Subject: Re: [PATCH net] tcp: disallow cwnd undo when switching congestion control
Date: Wed, 31 May 2017 11:47:32 -0700 [thread overview]
Message-ID: <20170531114732.1cfc4d79@xeon-e3> (raw)
In-Reply-To: <20170531182127.161289-1-ycheng@google.com>
On Wed, 31 May 2017 11:21:27 -0700
Yuchung Cheng <ycheng@google.com> wrote:
> When the sender switches its congestion control during loss
> recovery, if the recovery is spurious then it may incorrectly
> revert cwnd and ssthresh to the older values set by a previous
> congestion control. Consider a congestion control (like BBR)
> that does not use ssthresh and keeps it infinite: the connection
> may incorrectly revert cwnd to an infinite value when switching
> from BBR to another congestion control.
>
> This patch fixes it by disallowing such cwnd undo operation
> upon switching congestion control. Note that undo_marker
> is not reset s.t. the packets that were incorrectly marked
> lost would be corrected. We only avoid undoing the cwnd in
> tcp_undo_cwnd_reduction().
>
> Signed-off-by: Yuchung Cheng <ycheng@google.com>
> Signed-off-by: Soheil Hassas Yeganeh <soheil@google.com>
> Signed-off-by: Neal Cardwell <ncardwell@google.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
That looks correct. Are there other values of congestion state
that should be reset?
next prev parent reply other threads:[~2017-05-31 18:47 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-31 18:21 [PATCH net] tcp: disallow cwnd undo when switching congestion control Yuchung Cheng
2017-05-31 18:47 ` Stephen Hemminger [this message]
2017-05-31 19:47 ` Yuchung Cheng
2017-06-02 18:18 ` David Miller
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