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[83.245.236.31]) by smtp.gmail.com with ESMTPSA id h90-v6sm5590277ljf.65.2018.06.06.06.05.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Jun 2018 06:05:02 -0700 (PDT) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 11.3 \(3445.6.18\)) From: Jonathan Morton In-Reply-To: <36BE9775-A306-4DA3-B2D9-430FF07E391C@gmx.de> Date: Wed, 6 Jun 2018 16:04:59 +0300 Cc: Jonathan Foulkes , bloat Content-Transfer-Encoding: quoted-printable Message-Id: <3E669490-800E-40AE-B172-A99CB615822F@gmail.com> References: <152717340941.28154.812883711295847116.malone@soybean.canonical.com> <4f67f9b3-05a1-8d15-0aee-dfe8ea730d7c@gmail.com> <73c25a21-0ace-b5ee-090e-d06fb3b8dc60@kit.edu> <3F65061F-4F05-4F3F-8A43-FFCC1D27F585@gmail.com> <61E48C91-AEF9-4FF4-9F83-45EC7148EC54@jonathanfoulkes.com> <9675C88A-FCC0-43EB-9C71-CBEFD67408CB@gmx.de> <6AD85E99-BCD8-4548-AAA4-F5B08599C7AD@gmail.com> <36BE9775-A306-4DA3-B2D9-430FF07E391C@gmx.de> To: Sebastian Moeller X-Mailer: Apple Mail (2.3445.6.18) Subject: Re: [Bloat] [Bug 1436945] Re: devel: consider fq_codel as the default qdisc for networking 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: Wed, 06 Jun 2018 13:05:04 -0000 >>> The rationale for that decision still is valid, at low bandwidth = every opportunity to send a packet matters=E2=80=A6 >>=20 >> Yes, which is why the DRR++ algorithm is used to carefully choose = which flow to send a packet from. >=20 > Well, but look at it that way, the longer the traversal path after the = cake instance the higher the probability that the packet gets dropped by = a later hop. That's only true in case Cake is not at the bottleneck, in which case it = will only have a transient queue and AQM will disengage anyway. (This = assumes you're using an ack-clocked protocol, which TCP is.) >>> =E2=80=A6and every packet being transferred will increase the queued = packets delay by its serialization delay. >>=20 >> This is trivially true, but has no effect whatsoever on inter-flow = induced latency, only intra-flow delay, which is already managed = adequately well by an ECN-aware sender. >=20 > I am not sure that I am getting your point=E2=80=A6 Evidently. You've been following Cake development for how long, now? = This is basic stuff. > =E2=80=A6at 0.5Mbps every full-MTU packet will hog the line foe 20+ = milliseconds, so all other flows will incur at least that 20+ ms = additional latency, this is independent of inter- or intra-flow = perspective, no?. At the point where the AQM drop decision is made, Cake (and fq_codel) = has already decided which flow to service. On a bulk flow, most packets = are the same size (a full MTU), and even if the packet delivered is the = last one presently in the queue, probably another one will arrive by the = time it is next serviced - so the effect of the *flow's* presence = remains even into the foreseeable future. So there is no effect on other flows' latency, only subsequent packets = in the same flow - and the flow is always hurt by dropping packets, = rather than marking them. - Jonathan Morton