From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-x22a.google.com (mail-wm0-x22a.google.com [IPv6:2a00:1450:400c:c09::22a]) (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 E6BD23B2A3 for ; Fri, 28 Apr 2017 17:54:05 -0400 (EDT) Received: by mail-wm0-x22a.google.com with SMTP id u65so52385384wmu.1 for ; Fri, 28 Apr 2017 14:54:05 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-transfer-encoding; bh=ZA0RVINLd8QcV94bB9IXlwsTAZEZvzEVCzlLMBygXh8=; b=god4kxZU2LElCwxSaBOJrRbNXJo3hGqffTPlXF+T6LaaiKIPlOQ7h3b2EpkqT3PTLE PEVzUuJ0dbvLFdALd29pJCTOA6l5MiOXszgiTFQbeYozCysW2j8ekqBpFSb2g4zd1D3L GatcIryN+oY/eHO/MWJc0SZTok13ov1pcpGMv7jpViSD08OZkOAjiVaFA5CtZnGHhIr3 wCTGoFFoueXntIvmWYcsFmvSoDGZ5QWI1a6QtH5DTpfXi4Aq4stsTkirJdGwfZNqfqsx aA2q8TtbGa0SN+aJk4wTZhd3KjM7S92Q4Y0ccpvsoqbIrv3OqrauhCSwqQK5r93XttsK 8tYQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding; bh=ZA0RVINLd8QcV94bB9IXlwsTAZEZvzEVCzlLMBygXh8=; b=cK+1xJ9VC2qLFFObyAaYrca3FV1zhxB47OCR4Lf49nig7BHmYGZtn16SzogO7XM/1p +rB8FZafZGc0piWowZtMrDnyzyQvkgt5W70b9jn5lF7BMag252KJbc+HPVcfXj2gB+7i PYWYcrRxt08nfR0C8QHMg4EttAQF+0rEjnJOFlIzqLgKJ0jYT4iOMtNY61qdqx641FwF u8j3o/Xfx7FNpPsGXn2Cn+w2TVpmWm+rpXecCeB9WgUNC2O8vj8ovAZl5lvcAdqJsTHu eKwC7js+PfMCuxTjgwprqSz0zJ5M5Og7esI0QwgHf46OO8VBYTfoOjAipZI8UkzGwywk +L5A== X-Gm-Message-State: AN3rC/70jwnDWLNkZ6iIuJKRFeRx6OM1rTMSppSmlP85yi5NYhBnlHT+ dptI7hFMUpu84g== X-Received: by 10.28.65.65 with SMTP id o62mr120971wma.14.1493416444993; Fri, 28 Apr 2017 14:54:04 -0700 (PDT) Received: from [192.168.0.3] (185.182.7.51.dyn.plus.net. [51.7.182.185]) by smtp.gmail.com with ESMTPSA id o18sm9476012wrb.47.2017.04.28.14.54.03 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 28 Apr 2017 14:54:04 -0700 (PDT) To: David Lang , xnor Cc: Cake@lists.bufferbloat.net References: From: Andy Furniss Message-ID: <2bebaf69-a80a-9aa0-90b3-515686191d6a@gmail.com> Date: Fri, 28 Apr 2017 22:54:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:54.0) Gecko/20100101 Firefox/54.0 SeaMonkey/2.51a2 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Cake] cake default target is too low for bbr? X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 28 Apr 2017 21:54:06 -0000 David Lang wrote: > On Fri, 28 Apr 2017, xnor wrote: > >> As I understand it, increase in RTT due to queueing of packets is >> the main feedback mechanism for BBR. So dropping packets, which I >> already consider harmful, is really harmful with BBR because >> you're not telling the sender to slow down. > > If BBR does not slow down when packets are dropped, it's too hostile > to use on a public network. The only way for a public network to > respond to a flood of traffic higher than what it can handle is to > drop packets (with a possible warning via ECN shortly before packets > get dropped). If BBR doesn't slow down, it's just going to be > wasting bandwidth. > >> Instead, with a controlled delay qdisc like cake or codel, you're >> telling the sender to keep sending the data faster because the >> qdisc keeps the increase in RTT minimal. To make things worse, >> you're throwing away perfectly good packets with no effect other >> than wasting bandwidth. > > you are mistaking how cake and codel work. They are working at the > link endpoint adjacent to where the bandwidth is most limited. They > drop packets before they get send over the most contrained link. The > fact that the packets eat up some bandwidth on the non-constrained > link prior to the bottleneck doesn't matter, the bandwidth is > available by definition (otherwise it would be a constrained link to > the endpoint before it) Well cake may be used on ingress, OK so that is a "hack" but it's better than nothing. The ingress parameter does help a bit - but not much. Reducing bufferbloat is a good ideal, but it seems sometimes being too aggressive can hurt (I've also needed to increase rtt somewhat higher than the actual latency to get upstream tests to fill bandwidth). If target is supposed to work 5-10% of rtt value, then maybe cake could let users choose 10% rather than hard code 5% - to avoid the need to set excessive rtt values just to raise target.