From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lpp01m010-f43.google.com (mail-lpp01m010-f43.google.com [209.85.215.43]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id AEE2620069D for ; Fri, 6 Jan 2012 12:34:12 -0800 (PST) Received: by lagw12 with SMTP id w12so1210889lag.16 for ; Fri, 06 Jan 2012 12:34:10 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=subject:mime-version:content-type:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to:x-mailer; bh=XaQ28o+gyjqy/DknA9fFH5ONw2bHqq277z7b+DevLf8=; b=HqtblszR8G2MHzgHog2H9E6uoGcZq53tAftCiAi9H2ujLN3wiK/JykRpxU5oJ3pO++ XcfwTapsjUeztEA4FPHyb0NuQ1UiielcxyPKgsi9+Duf6s6OBNP4pbMWcIysqyfyJyD1 e+zbLpHas0D4vQ3AeUYK9ih0A3VEv8AFQ5fGY= Received: by 10.112.25.33 with SMTP id z1mr1449482lbf.7.1325882050172; Fri, 06 Jan 2012 12:34:10 -0800 (PST) Received: from [192.168.239.42] (xdsl-83-150-84-172.nebulazone.fi. [83.150.84.172]) by mx.google.com with ESMTPS id is1sm25325717lab.1.2012.01.06.12.34.08 (version=TLSv1/SSLv3 cipher=OTHER); Fri, 06 Jan 2012 12:34:09 -0800 (PST) Mime-Version: 1.0 (Apple Message framework v1084) Content-Type: text/plain; charset=us-ascii From: Jonathan Morton In-Reply-To: <201201051753.q05Hqx78012678@bagheera.jungle.bt.co.uk> Date: Fri, 6 Jan 2012 22:34:06 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: References: <1325481751.2526.23.camel@edumazet-laptop> <4F046F7B.6030905@freedesktop.org> <201201051753.q05Hqx78012678@bagheera.jungle.bt.co.uk> To: Bob Briscoe X-Mailer: Apple Mail (2.1084) Cc: bloat Subject: Re: [Bloat] What is fairness, anyway? was: Re: finally... winning on wired! X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 06 Jan 2012 20:34:13 -0000 On 5 Jan, 2012, at 7:52 pm, Bob Briscoe wrote: >> > 1: the 'slower flows gain priority' question is my gravest concern >> > (eg, ledbat, bittorrent). It's fixable with per-host FQ. >>=20 >> Meaning that you don't want to hand priority to stuff that is = intended >> to stay in the background? >=20 > The LEDBAT/BitTorrent issue wouldn't be fixed by per-host FQ. > LEDBAT/uTP tries to yield to other hosts, not just its own host. According to the LEDBAT I-D = (https://datatracker.ietf.org/doc/draft-ietf-ledbat-congestion/?include_te= xt=3D1), they expressly considered the effect of AQM and FQ, and = considered that even if they defeated the LEDBAT mechanism itself, it = didn't matter because they would achieve the LEDBAT *goal*. That goal is to avoid starving other flows, *not* to ensure that LEDBAT = flows would always be starved by others. > In fact, in the early part of the last decade, the whole issue of = long-running vs interactive flows showed how broken any form of FQ was. Wait, WTF? Isn't the long-running versus interactive problem precisely = what FQ *does* solve, by prioritising sparse flows over dense ones? We do need both per-flow and per-user fairness. SFQ and QFQ aim for = per-flow fairness, as currently implemented. Providers currently use a = variety of mechanisms - some more effective or more morally acceptable = than others - to implement per-user fairness. But there is currently no easy way for the latter to communicate with = the former - ECN doesn't count here - if the former is implemented at = the CPE, thereby reducing their effectiveness. Heck, I have to manually = configure my "router" (actually a computer) to know what the upload = bandwidth of the modem is. Why doesn't ECN count? Because the signalled packets come through the = wrong channel - flowing past the router and passing through a different = queue, facing in the opposite direction. The queue that needs to see = the information, doesn't. In any case, if ECN were already deployed = sufficiently well, the sending host would be backing off appropriately = and we wouldn't be talking about the problem here. - Jonathan Morton