netdev - Re: [PATCH v2 1/1] TCP: increase default initial receive window.

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Message-ID: <1292907606.2627.151.camel@edumazet-laptop>
Date:	Tue, 21 Dec 2010 06:00:06 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nandita Dukkipati <nanditad@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Tom Herbert <therbert@...gle.com>,
	Laurent Chavey <chavey@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Rick Jones <rick.jones2@...com>
Subject: Re: [PATCH v2 1/1] TCP: increase default initial receive window.

Le lundi 20 décembre 2010 à 16:15 -0800, Nandita Dukkipati a écrit :
> This patch changes the default initial receive window to 10 mss
> (defined constant). The default window is limited to the maximum
> of 10*1460 and 2*mss (when mss > 1460).
> 
> draft-ietf-tcpm-initcwnd-00 is a proposal to the IETF that recommends
> increasing TCP's initial congestion window to 10 mss or about 15KB.
> Leading up to this proposal were several large-scale live Internet
> experiments with an initial congestion window of 10 mss (IW10), where
> we showed that the average latency of HTTP responses improved by
> approximately 10%. This was accompanied by a slight increase in
> retransmission rate (0.5%), most of which is coming from applications
> opening multiple simultaneous connections. To understand the extreme
> worst case scenarios, and fairness issues (IW10 versus IW3), we further
> conducted controlled testbed experiments. We came away finding minimal
> negative impact even under low link bandwidths (dial-ups) and small
> buffers.  These results are extremely encouraging to adopting IW10.
> 
> However, an initial congestion window of 10 mss is useless unless a TCP
> receiver advertises an initial receive window of at least 10 mss.
> Fortunately, in the large-scale Internet experiments we found that most
> widely used operating systems advertised large initial receive windows
> of 64KB, allowing us to experiment with a wide range of initial
> congestion windows. Linux systems were among the few exceptions that
> advertised a small receive window of 6KB. The purpose of this patch is
> to fix this shortcoming.
> 
> References:
> 1. A comprehensive list of all IW10 references to date.
> http://code.google.com/speed/protocols/tcpm-IW10.html
> 
> 2. Paper describing results from large-scale Internet experiments with IW10.
> http://ccr.sigcomm.org/drupal/?q=node/621
> 
> 3. Controlled testbed experiments under worst case scenarios and a
> fairness study.
> http://www.ietf.org/proceedings/79/slides/tcpm-0.pdf
> 
> 4. Raw test data from testbed experiments (Linux senders/receivers)
> with initial congestion and receive windows of both 10 mss.
> http://research.csc.ncsu.edu/netsrv/?q=content/iw10
> 
> 5. Internet-Draft. Increasing TCP's Initial Window.
> https://datatracker.ietf.org/doc/draft-ietf-tcpm-initcwnd/
> 
> Signed-off-by: Nandita Dukkipati <nanditad@...gle.com>

Acked-by: Eric Dumazet <eric.dumazet@...il.com>


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