netdev - Re: [PATCH 4/4 net-next] tcp: use RTT from SACK for RTO

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Date:	Sun, 21 Jul 2013 23:40:07 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 4/4 net-next] tcp: use RTT from SACK for RTO

On Sun, Jul 21, 2013 at 1:39 AM, Yuchung Cheng <ycheng@...gle.com> wrote:
> If RTT is not available because Karn's check has failed or no
> new packet is acked, use the RTT measured from SACK to estimate
> the RTO. The sender can continue to estimate the RTO during loss
> recovery or reordering event upon receiving non-partial ACKs.
>
> This also changes when the RTO is re-armed. Previously it is
> only re-armed when some data is cummulatively acknowledged (i.e.,
> SND.UNA advances), but now it is re-armed whenever RTT estimator
> is updated. This feature is particularly useful to reduce spurious
> timeout for buffer bloat including cellular carriers [1], and
> RTT estimation on reordering events.
>
> [1] "An In-depth Study of LTE: Effect of Network Protocol and
>  Application Behavior on Performance", In Proc. of SIGCOMM 2013
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

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