netdev - Re: [PATCH net-next] tcp: fix bogus RTT for CC when retransmissions are acked

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Message-ID: <CADVnQyk7ZmB6OnCjpZqPy+7_OtUBLT0z_DszowEpu_UpMYpooA@mail.gmail.com>
Date:	Sun, 12 Apr 2015 10:13:33 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Kenneth Klette Jonassen <kennetkl@....uio.no>
Cc:	Netdev <netdev@...r.kernel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix bogus RTT for CC when retransmissions
 are acked

On Fri, Apr 10, 2015 at 8:17 PM, Kenneth Klette Jonassen
<kennetkl@....uio.no> wrote:
> Since retransmitted segments are not used for RTT estimation, previously
> SACKed segments present in the rtx queue are used. This estimation can be
> several times larger than the actual RTT. When a cumulative ack covers both
> previously SACKed and retransmitted segments, CC may thus get a bogus RTT.
>
> Such segments previously had an RTT estimation in tcp_sacktag_one(), so it
> seems reasonable to not reuse them in tcp_clean_rtx_queue() at all.
>
> Afaik, this has had no effect on SRTT/RTO because of Karn's check.
>
> Signed-off-by: Kenneth Klette Jonassen <kennetkl@....uio.no>

Acked-by: Neal Cardwell <ncardwell@...gle.com>
Tested-by: Neal Cardwell <ncardwell@...gle.com>

neal
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