From owner-freebsd-stable@FreeBSD.ORG  Tue Jul 12 10:21:24 2005
Return-Path: <owner-freebsd-stable@FreeBSD.ORG>
X-Original-To: freebsd-stable@freebsd.org
Delivered-To: freebsd-stable@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 84C9F16A41C;
	Tue, 12 Jul 2005 10:21:24 +0000 (GMT)
	(envelope-from demizu@dd.iij4u.or.jp)
Received: from r-dd.iij4u.or.jp (r-dd.iij4u.or.jp [210.130.0.70])
	by mx1.FreeBSD.org (Postfix) with ESMTP id DB6F343D48;
	Tue, 12 Jul 2005 10:21:23 +0000 (GMT)
	(envelope-from demizu@dd.iij4u.or.jp)
Received: from localhost (h062.p048.iij4u.or.jp [210.130.48.62])
	by r-dd.iij4u.or.jp (4U-MR/r-dd) id j6CAL9N4008834;
	Tue, 12 Jul 2005 19:21:11 +0900 (JST)
Date: Tue, 12 Jul 2005 19:20:42 +0900 (JST)
Message-Id: <20050712.192042.63502865.Noritoshi@Demizu.ORG>
From: Noritoshi Demizu <demizu@dd.iij4u.or.jp>
To: David Malone <dwmalone@maths.tcd.ie>
In-Reply-To: <200507121048.ab72454@salmon.maths.tcd.ie>
References: <E1DsGx9-0008Xc-GW@cs1.cs.huji.ac.il>
	<200507121048.ab72454@salmon.maths.tcd.ie>
X-Mailer: Mew version 4.1 on Emacs 21 / Mule 5.0 (SAKAKI)
Mime-Version: 1.0
Content-Type: Text/Plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Cc: freebsd-net@freebsd.org, freebsd-stable@freebsd.org,
	Luigi Rizzo <rizzo@icir.org>
Subject: Re: tcp troughput weirdness
X-BeenThere: freebsd-stable@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Production branch of FreeBSD source code <freebsd-stable.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>, 
	<mailto:freebsd-stable-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-stable>
List-Post: <mailto:freebsd-stable@freebsd.org>
List-Help: <mailto:freebsd-stable-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-stable>,
	<mailto:freebsd-stable-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Tue, 12 Jul 2005 10:21:24 -0000

(I am sorry if you have received this e-mail.  I'm resending this
 because it seems the previous one was lost.)

> TCP inflight limiting is supposed to guess the bandwidth-delay
> product for a TCP connection and stop the window expanding much
> above this.

(Just to clarify..)
TCP inflight limiting has a dedicated variable "snd_bwnd".
And min(tp->snd_wnd, tp->snd_cwnd, tp->snd_bwnd) limits
the amount of data to be sent.

> However, some of the guys I know that work on TCP dynamics reckon
> that they can they can come up with situations where inflight
> limiting will break. Unfortunately, I haven't had time to talk
> this through with them. I guess you may have found one of those
> situations ;-)

I experienced such situations with DragonFlyBSD.  I put examples
where inflight limiting reduces throughputs at the following pages.

  http://www.demizu.org/~noritosi/memo/2005/0706/
  http://www.demizu.org/~noritosi/memo/2005/0711/

Sorry, all senders in those examples are DragonFlyBSD.

Regards,
Noritoshi Demizu