From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-gg0-f171.google.com (mail-gg0-f171.google.com [209.85.161.171]) (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 C1370200681 for ; Wed, 9 May 2012 14:08:32 -0700 (PDT) Received: by ggki1 with SMTP id i1so936372ggk.16 for ; Wed, 09 May 2012 14:08:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:message-id:date:from:organization:user-agent:mime-version:to :cc:subject:references:in-reply-to:content-type :content-transfer-encoding; bh=uJjrrWDPIMzKJ2X4rv98IDc2sDJZ9ahw0slgib/QLvA=; b=jbLNTGlqxlzR75XgFZ7okNM5O3QzAKuvCV6W9ms77+lPgbOz2WhjejO2YZTZgTG/Jf BWWOhpvnGQixfwhqi9pQ0kpVs0aaAVwHRTg+h3pjEnG12ZQ23TzOCIZfnSswUBOdHsiu DC8kAeUq6LYjQic/VmGqT7Hf/2IcVkEGSz6BCmTVmWb9WkMz6XzCwYmzE/A/Ln1tPaSl MmEUzD3m9g9Gxyw+ogVJQY1LhDp3baQ80LMs3K2O30dEPEu4Wg4KKb6nZ9szObTxCqzF oeVQeQ/ZhPwbn2YwolBTh075S+Sn7c4OCsp46+47Oyot6H4Oj0byLjOYbCYEwWbttlil tzKQ== Received: by 10.236.75.4 with SMTP id y4mr2089323yhd.23.1336597711790; Wed, 09 May 2012 14:08:31 -0700 (PDT) Received: from [192.168.1.81] (c-50-138-162-108.hsd1.ma.comcast.net. [50.138.162.108]) by mx.google.com with ESMTPS id e3sm4891610anm.4.2012.05.09.14.08.30 (version=SSLv3 cipher=OTHER); Wed, 09 May 2012 14:08:31 -0700 (PDT) Sender: Jim Gettys Message-ID: <4FAADCCD.1060104@freedesktop.org> Date: Wed, 09 May 2012 17:08:29 -0400 From: Jim Gettys Organization: Bell Labs User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:12.0) Gecko/20120430 Thunderbird/12.0.1 MIME-Version: 1.0 To: Dave Taht References: <4FAAD534.2030100@superduper.net> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: codel@lists.bufferbloat.net Subject: Re: [Codel] Worst case conditions - large RTT X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 09 May 2012 21:08:33 -0000 On 05/09/2012 04:41 PM, Dave Taht wrote: > On Wed, May 9, 2012 at 1:36 PM, Simon Barber wrote: >> Codel assesses the minimum delay over a fixed time period (the interval) - >> what happens when the interval is much smaller that the RTT. For example a >> tcp stream is experiencing a 2 second RTT (perhaps due to bufferbloat at >> some point), yet the interval is 100ms. The TCP implementation is a poor one >> that will ACK a window at a time. Here codel will drop excessively, and >> cause low throughput? >> > One test I'd love to see is to compute from first principles what the latency and jitter we should now be observing in a single ideal TCP flow, at several RTT's. Then we can compare with that latency and jitter we *actually* observe. I'd expect a slightly higher value right now, as BQL's buffering is being added to the queue that CoDel is managing, but we can at least see if the implementation we have is behaving exactly as we would predict. - Jim