netdev - Re: [PATCH 1/3 net-next] tcp: refactor F-RTO

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Date:	Wed, 6 Mar 2013 16:05:15 -0500
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>,
	ilpo.jarvinen@...helsinki.fi, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3 net-next] tcp: refactor F-RTO

On Wed, Mar 6, 2013 at 3:52 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> The patch series refactor the F-RTO feature (RFC4138/5682).
>
> This is to simplify the loss recovery processing. Existing F-RTO
> was developed during the experimental stage (RFC4138) and has
> many experimental features.  It takes a separate code path from
> the traditional timeout processing by overloading CA_Disorder
> instead of using CA_Loss state. This complicates CA_Disorder state
> handling because it's also used for handling dubious ACKs and undos.
> While the algorithm in the RFC does not change the congestion control,
> the implementation intercepts congestion control in various places
> (e.g., frto_cwnd in tcp_ack()).
>
> The new code implements newer F-RTO RFC5682 using CA_Loss processing
> path.  F-RTO becomes a small extension in the timeout processing
> and interfaces with congestion control and Eifel undo modules.
> It lets congestion control (module) determines how many to send
> independently.  F-RTO only chooses what to send in order to detect
> spurious retranmission. If timeout is found spurious it invokes
> existing Eifel undo algorithms like DSACK or TCP timestamp based
> detection.
>
> The first patch removes all F-RTO code except the sysctl_tcp_frto is
> left for the new implementation.  Since CA_EVENT_FRTO is removed, TCP
> westwood now computes ssthresh on regular timeout CA_EVENT_LOSS event.
>
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>

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

neal
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