From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x233.google.com (mail-lj1-x233.google.com [IPv6:2a00:1450:4864:20::233]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 2BF0D3B29E for ; Tue, 9 Jul 2019 11:41:14 -0400 (EDT) Received: by mail-lj1-x233.google.com with SMTP id i21so20055301ljj.3 for ; Tue, 09 Jul 2019 08:41:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=2FjdbXAz/FJzIp0q0XX2KwDHU4oS9dOUuy/3LBUrCRo=; b=DyYRn8TxutrLH04/YPnFe6ap32NlyMLhL/A2TzjAYklvAS7BgjA3ZTxPBwYVqKxtJg wJEssU2uRv3ppnc1JSsgXKxp7C5R3kzmDzIZVPSo9i/C9A8ejagXNFvcBIounDVanGc/ 2d40oq0FGALXFcHXxcVCXtsLP25+gIlbMzdJ5yF7olYo1NNpOktnAZ493DJEcg9EPWmc Z0/h3YZZabqL28ELhMoMiQJaMZH93dHjJALe8n5HiRco7esAGBJPahZIOGUgmiWi1sfx G2RxABvA5C8yUUCLffjg8Tx8rnHgCrmCMUMFJbqbWepEbRCA5xswxWNHR0QFgieR5e+I StBg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=2FjdbXAz/FJzIp0q0XX2KwDHU4oS9dOUuy/3LBUrCRo=; b=ArcxGM5sdVktM0YFnhfEllDTAA3cnPHTw8QXExT+8a4aAJPup5gUEtQixTy1fY9p+h vSQZ+xTRoMZxB7vFOTwAcTvoeUS3iFeK4KtGscQsSd6qgxznw+BpmuLZsKAseNwrscwk pXVGT1vnWRAfd7qcho6o9XZquWu3M14h7vHF/zLwU+riCrc8Rq/Slb8jkBp3YgxU+zkf AIi2aZkP28KyAaRElL7ynqLJZlrtRbBzYsvGG0u1JptHy6iw3YIfrM5tqOxwLdRCpZFD W+yn2dz2DUTSeEE8aWx+9xBkhyN7iRzd2VMDhW5Y6t+SEtOJu6oWYTQbZ+XEn6ormLLg RzuQ== X-Gm-Message-State: APjAAAUPoAr3nqEUiuKMF97EGMLimeNIcFDw++r77MJYV/gjM07PLP4k EvxpkOzPVHeCpuEteVGWkefKTNUS X-Google-Smtp-Source: APXvYqw3Bh1wcXv3ifpN6COW8NwV9ITaeKmis5u5jAIaM86zFvnjvfdDJ7Ree+RRxpil2NzkCLadlA== X-Received: by 2002:a2e:8559:: with SMTP id u25mr14094250ljj.224.1562686873072; Tue, 09 Jul 2019 08:41:13 -0700 (PDT) Received: from jonathartonsmbp.lan (83-245-234-41-nat-p.elisa-mobile.fi. [83.245.234.41]) by smtp.gmail.com with ESMTPSA id u22sm4901510ljd.18.2019.07.09.08.41.11 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 09 Jul 2019 08:41:12 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) From: Jonathan Morton In-Reply-To: <24f7b15a-129f-ca44-60e0-32c7d23eadf4@bobbriscoe.net> Date: Tue, 9 Jul 2019 18:41:10 +0300 Cc: "ecn-sane@lists.bufferbloat.net" , tcpm IETF list , tsvwg IETF list Content-Transfer-Encoding: quoted-printable Message-Id: References: <24f7b15a-129f-ca44-60e0-32c7d23eadf4@bobbriscoe.net> To: Bob Briscoe X-Mailer: Apple Mail (2.3445.9.1) Subject: Re: [Ecn-sane] ECN CE that was ECT(0) incorrectly classified as L4S X-BeenThere: ecn-sane@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Discussion of explicit congestion notification's impact on the Internet List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Jul 2019 15:41:14 -0000 > On 13 Jun, 2019, at 7:48 pm, Bob Briscoe wrote: >=20 > 1. It is quite unusual to experience queuing at more than one > bottleneck on the same path (the available capacities have = to > be identical). Following up on David Black's comments, I'd just like to note that the = above is not the true criterion for multiple sequential queuing. Many existing TCP senders are unpaced (aside from ack-clocking), = including FreeBSD, resulting in potentially large line-rate bursts at = the origin - especially during slow-start. Even in congestion = avoidance, each ack will trigger a closely spaced packet pair (or = sometimes a triplet). It is then easy to imagine, or to build a testbed = containing, an arbitrarily long sequence of consecutively narrower = links; upon entering each, the burst of packets will briefly collect in = a queue and then be paced out at the new rate. TCP pacing does largely eliminate these bursts when implemented = correctly. However, Linux' pacing and IW is specifically (and = apparently deliberately) set up to issue a 10-packet line-rate burst on = startup. This effect has shown up in SCE tests to the point where we = had to patch this behaviour out of the sending kernel to prevent an = instant exit from slow-start. - Jonathan Morton