From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from iramx2.ira.uni-karlsruhe.de (iramx2.ira.uni-karlsruhe.de [141.3.10.81]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 9998B3B29E for ; Tue, 27 Nov 2018 05:35:01 -0500 (EST) Received: from i72vorta.tm.uni-karlsruhe.de ([141.3.71.26] helo=i72vorta.tm.kit.edu) by iramx2.ira.uni-karlsruhe.de with esmtp port 25 iface 141.3.10.81 id 1gRaho-00063B-Qp; Tue, 27 Nov 2018 11:35:00 +0100 Received: from [IPv6:::1] (ip6-localhost [IPv6:::1]) by i72vorta.tm.kit.edu (Postfix) with ESMTPS id C3678420DD3; Tue, 27 Nov 2018 11:35:00 +0100 (CET) To: Luca Muscariello Cc: Jonathan Morton , bloat References: <65EAC6C1-4688-46B6-A575-A6C7F2C066C5@heistp.net> From: "Bless, Roland (TM)" Openpgp: preference=signencrypt Autocrypt: addr=roland.bless@kit.edu; prefer-encrypt=mutual; keydata= xsFNBFi0OxABEACy2VohJ7VhSu/xPCt4/6qCrw4Pw2nSklWPfAYEk1QgrbiwgvLAP9WEhAIU w45cojBaDxytIGg8eaYeIKSmsXjHGbV/ZTfo8r11LX8yPYR0WHiMWZpl0SHUd/CZIkv2pChO 88vF/2FKN95HDcp24pwONF4VhxJoSFk6c0mDNf8Em/Glt9BcWX2AAvizTmpQDshaPje18WH3 4++KwPZDd/sJ/hHSXiPg1Gdhs/OG/C0CJguOAlqbgSVAe3qKOr1M4K5M+wVpsk373pXRfxd7 ZAmZ05iBTn+LfgVcz+AfaKKcsWri5CdTT+7JDL6QNQpox+b5FXZFSHnEIST+/qzfG7G2LqqY mml6TYY8XbaNyXZP0QKncfSpRx8uTRWReHUa1YbSuOxXYh6bXpcugD25mlC/Lu0g7tz4ijiK iIwq9+P2H1KfAAfYyYZh6nOoE6ET0TjOjUSa+mA8cqjPWX99kEEgf1Xo+P9fx9QLCLWIY7zc mSM+vjQKgdUFpMSCKcYEKOuwlPuOz8bVECafxaEtJJHjCOK8zowe2eC9OM+G+bmtAO3qYcYZ hQ/PV3sztt/PjgdtnFAYPFLc9189rHRxKsWSOb4xPkRw/YQAI9l15OlUEpsyOehxmAmTsesn tSViCz++PCdeXrQc1BCgl8nDytrxW+n5w1aaE8aL3hn8M0tonQARAQABzShSb2xhbmQgQmxl c3MgKFRNKSA8cm9sYW5kLmJsZXNzQGtpdC5lZHU+wsGABBMBCAAqAhsDBQkSzAMABQsJCAcC BhUICQoLAgQWAgMBAh4BAheABQJYtYdHAhkBAAoJEKON2tlkOJXuzWkP+wfjUnDNzRm4r34a AMWepcQziTgqf4I1crcL6VD44767HhyFsjcKH31E5G5gTDxbpsM4pmkghKeLrpPo30YK3qb7 E9ifIkpJTvMu0StSUmcXq0zPyHZ+HxHeMWkosljG3g/4YekCqgWwrB62T7NMYq0ATQe1MGCZ TAPwSPGCUZT3ioq50800FMI8okkGTXS3h2U922em7k8rv7E349uydv19YEcS7tI78pggMdap ASoP3QWB03tzPKwjqQqSevy64uKDEa0UgvAM3PRbJxOYZlX1c3q/CdWwpwgUiAhMtPWvavWW Tcw6Kkk6e0gw4oFlDQ+hZooLv5rlYR3egdV4DPZ1ugL51u0wQCQG9qKIMXslAdmKbRDkEcWG Oi2bWAdYyIHhhQF5LSuaaxC2P2vOYRHnE5yv5KTV3V7piFgPFjKDW+giCRd7VGfod6DY2b2y zwidCMve1Qsm8+NErH6U+hMpMLeCJDMu1OOvXYbFnTkqjeg5sKipUoSdgXsIo4kl+oArZlpK qComSTPhij7rMyeu/1iOwbNCjtiqgb55ZE7Ekd84mr9sbq4Jm/4QGnVI30q4U2vdGSeNbVjo d1nqjf3UNzP2ZC+H9xjsCFuKYbCX6Yy4SSuEcubtdmdBqm13pxua4ZqPSI0DQST2CHC7nxL1 AaRGRYYh5zo2vRg3ipkEzsFNBFi0OxABEAC2CJNp0/Ivkv4KOiXxitsMXZeK9fI0NU2JU1rW 04dMLF63JF8AFiJ6qeSL2mPHoMiL+fG5jlxy050xMdpMKxnhDVdMxwPtMiGxbByfvrXu18/M B7h+E1DHYVRdFFPaL2jiw+Bvn6wTT31MiuG9Wh0WAhoW8jY8IXxKQrUn7QUOKsWhzNlvVpOo SjMiW4WXksUA0EQVbmlskS/MnFOgCr8q/FqwC81KPy+VLHPB9K/B65uQdpaw78fjAgQVQqpx H7gUF1EYpdZWyojN+V8HtLJx+9yWAZjSFO593OF3/r0nDHEycuOjhefCrqr0DDgTYUNthOdU KO2CzT7MtweRtAf0n27zbwoYvkTviIbR+1lV1vNkxaUtZ6e1rtOxvonRM1O3ddFIzRp/Qufu HfPe0YqhEsrBIGW1aE/pZW8khNQlB6qt20snL9cFDrnB6+8kDG3e//OjK1ICQj9Y/yyrJVaX KfPbdHhLpsgh8TMDPoH+XXQlDJljMD0++/o7ckO3Sfa8Zsyh1WabyKQDYXDmDgi9lCoaQ7Lf uLUpoMvJV+EWo0jE4RW/wBGQbLJp5usy5i0fhBKuDwsKdLG3qOCf4depIcNuja6ZmZHRT+3R FFjvZ/dAhrCWpRTxZANlWlLZz6htToJulAZQJD6lcpVr7EVgDX/y4cNwKF79egWXPDPOvQAR AQABwsFlBBgBCAAPBQJYtDsQAhsMBQkSzAMAAAoJEKON2tlkOJXukMoP/jNeiglj8fenH2We 7SJuyBp8+5L3n8eNwfwY5C5G+etD0E6/lkt/Jj9UddTazxeB154rVFXRzmcN3+hGCOZgGAyV 1N7d8xM6dBqRtHmRMPu5fUxfSqrM9pmqAw2gmzAe0eztVvaM+x5x5xID2WZOiOq8dx9KOKrp Zorekjs3GEA3V1wlZ7Nksx/o8KZ04hLeKcR1r06zEDLN/yA+Fz8IPa0KqpuhrL010bQDgAhe 9o5TA0/cMJpxpLqHhX2As+5cQAhKDDsWJu3oBzZRkN7Hh/HTpWurmTQRRniLGSeiL0zdtilX fowyxGXH6QWi3MZYmpOq+etr7o4EGGbm2inxpVbM+NYmaJs+MAi/z5bsO/rABwdM5ysm8hwb CGt+1oEMORyMcUk/uRjclgTZM1NhGoXm1Un67+Rehu04i7DA6b8dd1H8AFgZSO2H4IKi+5yA Ldmo+ftCJS83Nf6Wi6hJnKG9aWQjKL+qmZqBEct/D2uRJGWAERU5+D0RwNV/i9lQFCYNjG9X Tew0BPYYnBtHFlz9rJTqGhDu4ubulSkbxAK3TIk8XzKdMvef3tV/7mJCmcaVbJ2YoNUtkdKJ goOigJTMBXMRu4Ibyq1Ei+d90lxhojKKlf9yguzpxk5KYFGUizp0dtvdNuXRBtYrwzykS6vB zTlLqHZ0pvGjNfTSvuuN Organization: Institute of Telematics, Karlsruhe Institute of Technology Message-ID: <86b16a95-e47d-896b-9d43-69c65c52afc7@kit.edu> Date: Tue, 27 Nov 2018 11:35:00 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 8bit X-ATIS-AV: ClamAV (iramx2.ira.uni-karlsruhe.de) X-ATIS-Timestamp: iramx2.ira.uni-karlsruhe.de 1543314900.893976732 Subject: Re: [Bloat] when does the CoDel part of fq_codel help in the real world? 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: Tue, 27 Nov 2018 10:35:01 -0000 Hi, Am 27.11.18 um 11:29 schrieb Luca Muscariello: > I have never said that you need to fill the buffer to the max size to > get full capacity, which is an absurdity. Yes, it's absurd, but that's what today's loss-based CC algorithms do. > I said you need at least the BDP so that the queue never empties out. > The link is fully utilized IFF the queue is never emptied. I was also a bit imprecise: you'll need a BDP in flight, but you don't need to fill the buffer at all. The latter sentence is valid only in the direction: queue not empty -> link fully utilized. Regards, Roland > > > > On Tue 27 Nov 2018 at 11:26, Bless, Roland (TM) > wrote: > > Hi Luca, > > Am 27.11.18 um 10:24 schrieb Luca Muscariello: > > A congestion controlled protocol such as TCP or others, including > QUIC, > > LEDBAT and so on > > need at least the BDP in the transmission queue to get full link > > efficiency, i.e. the queue never empties out. > > This is not true. There are congestion control algorithms > (e.g., TCP LoLa [1] or BBRv2) that can fully utilize the bottleneck link > capacity without filling the buffer to its maximum capacity. The BDP > rule of thumb basically stems from the older loss-based congestion > control variants that profit from the standing queue that they built > over time when they detect a loss: > while they back-off and stop sending, the queue keeps the bottleneck > output busy and you'll not see underutilization of the link. Moreover, > once you get good loss de-synchronization, the buffer size requirement > for multiple long-lived flows decreases. > > > This gives rule of thumbs to size buffers which is also very practical > > and thanks to flow isolation becomes very accurate. > > The positive effect of buffers is merely their role to absorb > short-term bursts (i.e., mismatch in arrival and departure rates) > instead of dropping packets. One does not need a big buffer to > fully utilize a link (with perfect knowledge you can keep the link > saturated even without a single packet waiting in the buffer). > Furthermore, large buffers (e.g., using the BDP rule of thumb) > are not useful/practical anymore at very high speed such as 100 Gbit/s: > memory is also quite costly at such high speeds... > > Regards, >  Roland > > [1] M. Hock, F. Neumeister, M. Zitterbart, R. Bless. > TCP LoLa: Congestion Control for Low Latencies and High Throughput. > Local Computer Networks (LCN), 2017 IEEE 42nd Conference on, pp. > 215-218, Singapore, Singapore, October 2017 > http://doc.tm.kit.edu/2017-LCN-lola-paper-authors-copy.pdf > > > Which is:  > > > > 1) find a way to keep the number of backlogged flows at a > reasonable value.  > > This largely depends on the minimum fair rate an application may > need in > > the long term. > > We discussed a little bit of available mechanisms to achieve that > in the > > literature. > > > > 2) fix the largest RTT you want to serve at full utilization and size > > the buffer using BDP * N_backlogged.   > > Or the other way round: check how much memory you can use  > > in the router/line card/device and for a fixed N, compute the largest > > RTT you can serve at full utilization.  > > > > 3) there is still some memory to dimension for sparse flows in > addition > > to that, but this is not based on BDP.  > > It is just enough to compute the total utilization of sparse flows and > > use the same simple model Toke has used  > > to compute the (de)prioritization probability. > > > > This procedure would allow to size FQ_codel but also SFQ. > > It would be interesting to compare the two under this buffer sizing.  > > It would also be interesting to compare another mechanism that we have > > mentioned during the defense > > which is AFD + a sparse flow queue. Which is, BTW, already > available in > > Cisco nexus switches for data centres. > > > > I think that the the codel part would still provide the ECN feature, > > that all the others cannot have. > > However the others, the last one especially can be implemented in > > silicon with reasonable cost. >