From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [IPv6:2a00:1450:4864:20::129]) (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 73DF93B29D for ; Mon, 11 Oct 2021 02:10:52 -0400 (EDT) Received: by mail-lf1-x129.google.com with SMTP id y26so69550071lfa.11 for ; Sun, 10 Oct 2021 23:10:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=qUIW1o57FKZLboDnLRU2/2RUlTjNBGIjwZo+IhSIpOw=; b=LppPgYOIf1shj61PRvkiju2ol+x/U3pz5U+/4W5ptVmoit5u5k1nFvreqRG2gergME ZfA6MeXnfdZ8BVCH9QFnC3LkAayI8ELgapz+AOdZFerH1kku+SaPLl04BYFVaKzhKvzz /M2V9Z/4rfRi/cMJR6otH8xpqB8+zgPwnt7+3Bx6zZX69e/vzcVscu5qgL6Nh8Cd1kOb BQm5MtG8YwU3vi9N6MGlKdq4D2IVi/neHeFKCIWYkK/WAc/FEw+9VAx0uTUxxu/UFEGG P9uIrGFxTLoSwlocm9+UMH8NbwQRnq5Dq3iqw10BqngA2EnjUdc4WrlUjdIej22SuT/H AtzQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=qUIW1o57FKZLboDnLRU2/2RUlTjNBGIjwZo+IhSIpOw=; b=t6lViBxLUoER9JTFd24P7smTs53MNED7/+61BYEfJ7+Uo++JbKz4jia0h4aVg+Q23u vUQ9P/yN6SERrAkPpXPQRh/Fs9UveFhcsaBdSVhB6QuJ/SGdtrvEc9j4AOyCsu6Mcb7r e4XQ97pho+NraFrygiP3UapwZnBwZnGJHXZmJRjqFVQed6OxSOiEMIbvZTLeFYyQf5Pm C924HkUt95zS/qglgHPTl7604UjtDYBoRwnknbNu8MYHiYW7pjoRTdTFR10HjQfBm6LF yhiyMsXNPsQEITCZqzeOR0jcVsZfHvg85UEPJI2u2ACGni4APYUxigwB31Y5TsNrrzEn EJKQ== X-Gm-Message-State: AOAM5301G3xQ+sJM8DgudXuSV7YqwKY0cPzsmNWLB1OnRQibvLukwJ1G Q88tuJWPJ+7xkEAqs4+kCfc= X-Google-Smtp-Source: ABdhPJxun5cujDSmEGZ1viVHEWsWxu64tk9xGRou4FoPBNlNOWxbL4NWu33xW6Izi55Cepl7Rhtcmg== X-Received: by 2002:a2e:a4b2:: with SMTP id g18mr19557721ljm.275.1633932649693; Sun, 10 Oct 2021 23:10:49 -0700 (PDT) Received: from smtpclient.apple (176-93-88-52.bb.dnainternet.fi. [176.93.88.52]) by smtp.gmail.com with ESMTPSA id w6sm692766lfk.200.2021.10.10.23.10.48 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Sun, 10 Oct 2021 23:10:49 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 14.0 \(3654.100.0.2.22\)) From: Jonathan Morton In-Reply-To: Date: Mon, 11 Oct 2021 09:10:47 +0300 Cc: bloat Content-Transfer-Encoding: quoted-printable Message-Id: References: To: Dave Taht X-Mailer: Apple Mail (2.3654.100.0.2.22) Subject: Re: [Bloat] updating the theory of buffer sizing X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 11 Oct 2021 06:10:52 -0000 > On 10 Oct, 2021, at 8:48 pm, Dave Taht wrote: >=20 > This latest from Nick & co, was quite good: >=20 > https://arxiv.org/pdf/2109.11693.pdf Skip the false modesty - I think this is very important work, actually. = I would expect it to get cited a heck of a lot in future work, both in = academia and in the IETF. In terms of its content, it confirms, contextualises, and formalises = various things that I already understood at an intuitive level. The = mathematics involved is simple and accessible (unlike some papers I've = read recently), and the practical explanations of the observed = behaviours are clear and to the point. I particularly appreciate the = way they were able to parameterise certain characteristics on a = continuum, rather than all-or-nothing, as that captures the complex = characteristics of real traffic much better. The observations about synchronisation of congestion responses are also = very helpful. When synchronised, the aggregate behaviour of many flows = is similar to that of a much smaller number, perhaps even a single flow. = When desynchronised, the well-known statistical multiplexing effects = apply. They also clearly explain why the "hard threshold" type of ECN = marking is undesirable - because it provokes synchronisation in a way = that tail-drop does not (and this is also firmly related to a point we = discussed last week). Notably, they started seeing the effects of burstiness, on a small and = theoretically "smooth" network, on timescales of approximately a seventh = of a millisecond (20 packets, 9000 byte MTU, 10Gbps). They were unable = to reduce buffer sizes below that level without throughput dropping well = below their theoretical predictions, which had held true down to that = point. This has implications for setting AQM targets and tolerances in = even near-ideal network environments. But they did also note that BBR = showed much less sensitivity to this effect, as it uses pacing. In any = case, it confirms that the first role of a buffer is to absorb bursts = without excessive loss. - Jonathan Morton=