netdev - Re: [PATCH net-next] tcp: properly handle stretch acks in slow start

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Message-Id: <20131104.195826.303744401862156515.davem@davemloft.net>
Date:	Mon, 04 Nov 2013 19:58:26 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	ycheng@...gle.com
Cc:	netdev@...r.kernel.org, edumazet@...gle.com, ncardwell@...gle.com,
	vanj@...gle.com
Subject: Re: [PATCH net-next] tcp: properly handle stretch acks in slow
 start

From: Yuchung Cheng <ycheng@...gle.com>
Date: Thu, 31 Oct 2013 11:07:31 -0700

> Slow start now increases cwnd by 1 if an ACK acknowledges some packets,
> regardless the number of packets. Consequently slow start performance
> is highly dependent on the degree of the stretch ACKs caused by
> receiver or network ACK compression mechanisms (e.g., delayed-ACK,
> GRO, etc).  But slow start algorithm is to send twice the amount of
> packets of packets left so it should process a stretch ACK of degree
> N as if N ACKs of degree 1, then exits when cwnd exceeds ssthresh. A
> follow up patch will use the remainder of the N (if greater than 1)
> to adjust cwnd in the congestion avoidance phase.
> 
> In addition this patch retires the experimental limited slow start
> (LSS) feature. LSS has multiple drawbacks but questionable benefit. The
> fractional cwnd increase in LSS requires a loop in slow start even
> though it's rarely used. Configuring such an increase step via a global
> sysctl on different BDPS seems hard. Finally and most importantly the
> slow start overshoot concern is now better covered by the Hybrid slow
> start (hystart) enabled by default.
> 
> Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
> Signed-off-by: Neal Cardwell <ncardwell@...gle.com>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied.
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