From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf1-x12c.google.com (mail-lf1-x12c.google.com [IPv6:2a00:1450:4864:20::12c]) (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 47E653B2A4; Thu, 8 Jul 2021 10:40:52 -0400 (EDT) Received: by mail-lf1-x12c.google.com with SMTP id p1so16280645lfr.12; Thu, 08 Jul 2021 07:40:52 -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=O92bAjri69mlfpH4Ntt46UC62OvibeOey0NRfeclyns=; b=ZUboetXk/s64t3wcO7Rn670x4joEifujH+iakGiuV/LXtGBME/ikbQy5dvMOlOrD0J gFiX+RjObGwuY2aqxZJbJxf9jkHEFdZ6XhTuolmIQQG+3Rr8k5RWVutXvJX/lRlm5v50 pF74G/7A3l1M1lQkdVP93eB9UKanVJ1mUFyZe53q5UUxL/L1lhNr84jryHkQGNBD3nJg EvaABqdnD3oOTH7H2s2js5q99zjUxnLsUCG8xotk4waf9iPxEHizevOb4L15vXs8RAkv mYiR34csO00hIHb2QLRuIzG20kB1Hi3lQCDK5OBb8TXz90BgOm2itcwkX8fg17R+rhHa LQvA== 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=O92bAjri69mlfpH4Ntt46UC62OvibeOey0NRfeclyns=; b=VTGDOn6G1/BGZPlPCvBlGbs34uBLmW3DxVNCBlkFsY30cc9wfJ2G6KnUJYJPh4uzoc 2iiuwMxq5brmXJwOCjbT/VYeVSRRPHfTZ+UoWBMMUglVG/O3I7akwsSHp4f73j5SHMnV 3/c6QAqT5xU+qTrzRM+pjTFsNnL5uEVKvo8zT/bzrVck1QSCEhR0gEyxyQWheuM120Ul 3zVAsTNvtNbI1CrMi5pcXmq6PbcDLlyDFWdO+5KvnuwpmyEFbzoIXLQfaPlMwVUcAZSE mxFCQDaZrkFiGJBenwVJiG8gVThQAhOh/RHUGMqPyLeatfMsJNWkkweZfgO3tQwcjvHm SfNw== X-Gm-Message-State: AOAM532LkdzlG7IQh5AKrPyL+Sx4ydhj6l9ro73ly8DWiqawZUYNvqLH bOx9kygLNStenetfvR8q2Qc= X-Google-Smtp-Source: ABdhPJzrRcdLn53T0N6BNDJKQnnlhVKPR/wNxCzwEPNmm+utteopdoGXXsFcDnuD1flSVx/12I+ozQ== X-Received: by 2002:a2e:8090:: with SMTP id i16mr15629778ljg.422.1625755251047; Thu, 08 Jul 2021 07:40:51 -0700 (PDT) Received: from jonathartonsmbp.lan (37-136-219-147.rev.dnainternet.fi. [37.136.219.147]) by smtp.gmail.com with ESMTPSA id n26sm213088lfe.212.2021.07.08.07.40.49 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 08 Jul 2021 07:40:50 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.7\)) From: Jonathan Morton In-Reply-To: Date: Thu, 8 Jul 2021 17:40:47 +0300 Cc: "Bless, Roland (TM)" , "cerowrt-devel@lists.bufferbloat.net" , bloat Content-Transfer-Encoding: quoted-printable Message-Id: <7175CC77-9B2B-4431-BF47-21F68CA29D26@gmail.com> References: <55fdf513-9c54-bea9-1f53-fe2c5229d7ba@eggo.org> <871t4as1h9.fsf@toke.dk> <3D32F19B-5DEA-48AD-97E7-D043C4EAEC51@gmail.com> <1465267957.902610235@apps.rackspace.com> <20210702095924.0427b579@hermes.local> <1bab95a0-7904-2807-02fe-62674c19948f@kit.edu> <393e9ca6-f9f3-1826-9fbc-6d36871223d8@kit.edu> To: Matt Mathis X-Mailer: Apple Mail (2.3445.9.7) Subject: Re: [Bloat] Abandoning Window-based CC Considered Harmful (was Re: Bechtolschiem) 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: Thu, 08 Jul 2021 14:40:52 -0000 > On 8 Jul, 2021, at 4:29 pm, Matt Mathis via Bloat = wrote: >=20 > That said, it is also true that multi-stream BBR behavior is quite = complicated and needs more queue space than single stream. This = complicates the story around the traditional workaround of using = multiple streams to compensate for Reno & CUBIC lameness at larger = scales (ordinary scales today). Multi-stream does not help BBR = throughput and raises the queue occupancy, to the detriment of other = users. I happen to think that using multiple streams for the sake of maximising = throughput is the wrong approach - it is a workaround employed = pragmatically by some applications, nothing more. If BBR can do just as = well using a single flow, so much the better. Another approach to improving the throughput of a single flow is = high-fidelity congestion control. The L4S approach to this, derived = rather directly from DCTCP, is fundamentally flawed in that, not being = fully backwards compatible with ECN, it cannot safely be deployed on the = existing Internet. An alternative HFCC design using non-ambiguous signalling would be = incrementally deployable (thus applicable to Internet scale) and = naturally overlaid on existing window-based congestion control. It's = possible to imagine such a flow reaching optimal cwnd by way of = slow-start alone, then "cruising" there in a true equilibrium with = congestion signals applied by the network. In fact, we've already shown = this occurring under lab conditions; in other cases it still takes one = CUBIC cycle to get there. BBR's periodic probing phases would not be = required here. > IMHO, two approaches seem to be useful: > a) congestion-window-based operation with paced sending > b) rate-based/paced sending with limiting the amount of inflight data So this corresponds to approach a) in Roland's taxonomy. - Jonathan Morton=