netdev - Re: [PATCH net] tcp: do not rearm RTO when future data are sacked

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Date:	Thu, 24 Oct 2013 13:03:18 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	Yuchung Cheng <ycheng@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Lawrence Brakmo <brakmo@...gle.com>,
	Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net] tcp: do not rearm RTO when future data are sacked

On Thu, Oct 24, 2013 at 11:59 AM, Yuchung Cheng <ycheng@...gle.com> wrote:
> Patch ed08495c3 "tcp: use RTT from SACK for RTO" always re-arms RTO upon
> obtaining a RTT sample from newly sacked data.
>
> But technically RTO should only be re-armed when the data sent before
> the last (re)transmission of write queue head are (s)acked. Otherwise
> the RTO may continue to extend during loss recovery on data sent
> in the future.
>
> Note that RTTs from ACK or timestamps do not have this problem, as the RTT
> source must be from data sent before.
>
> The new RTO re-arm policy is
> 1) Always re-arm RTO if SND.UNA is advanced
> 2) Re-arm RTO if sack RTT is available, provided the sacked data was
>    sent before the last time write_queue_head was sent.
>
> Signed-off-by: Larry Brakmo <brakmo@...gle.com>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> ---
>  net/ipv4/tcp_input.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)

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

neal
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