From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lf0-x233.google.com (mail-lf0-x233.google.com [IPv6:2a00:1450:4010:c07::233]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 4722E21F536 for ; Tue, 3 Nov 2015 09:00:29 -0800 (PST) Received: by lfgh9 with SMTP id h9so25323966lfg.1 for ; Tue, 03 Nov 2015 09:00:27 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=content-type:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=ySq+M+3+szE1epxbuv2lHNM8Jg6ufZ4/IB9CYijofqY=; b=0HZwdQ1uFybmWnFlyIaZKEsbVpoQ9tip4cEjlVMz2IGVp2bTifeUsvxalZX4FWjFri j63Y0qls3o4JOe94s2c4tc4MJwI9/2WkGdnzR5BXuiYTgoRXn8XmcXpRQFKpKC2r8ry4 /3c3Sjt/ClHZHbwYKTWgp902pSE2hIu3eW6Wk0gS5uMaxy+UX7rNedX7cDLk2sU35UER aNidpV4UvofF74HqgKIzVe5kI8Kyjg7yK0SeyJoaw3Xzpb4ReemvoZ3T58yooJsNHYip WF5zu02oVTBEm0xU/zxeuqC6iPme/Ez4ISwMPCb+DF11G68uCFvE6dgW7T650MxcKL5Z tW1g== X-Received: by 10.112.157.166 with SMTP id wn6mr11031962lbb.30.1446570027471; Tue, 03 Nov 2015 09:00:27 -0800 (PST) Received: from bass.home.chromatix.fi (83-245-237-115-nat-p.elisa-mobile.fi. [83.245.237.115]) by smtp.gmail.com with ESMTPSA id j9sm4927915lbc.19.2015.11.03.09.00.26 (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 03 Nov 2015 09:00:26 -0800 (PST) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 9.1 \(3096.5\)) From: Jonathan Morton In-Reply-To: <274D3A0FA900FD47AA6B56991AAA32FDC5430D9E@wtl-exchp-1.sandvine.com> Date: Tue, 3 Nov 2015 19:00:24 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: References: <201311122230.rACMUBmH003536@bagheera.jungle.bt.co.uk> <87wpzfpbd3.fsf@alrua-karlstad.karlstad.toke.dk> <56045CA8.2060103@bobbriscoe.net> <560BA261.6020206@bobbriscoe.net> <560BDED0.1080402@bobbriscoe.net> <274D3A0FA900FD47AA6B56991AAA32FDC5430D9E@wtl-exchp-1.sandvine.com> To: Jeff Weeks X-Mailer: Apple Mail (2.3096.5) Cc: Andrew Mcgregor , Bob Briscoe , codel@lists.bufferbloat.net, Van Jacobson , AQM IETF list , Dave Dolson Subject: Re: [Codel] [aqm] CoDel's control law that determines drop frequency 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: Tue, 03 Nov 2015 17:00:52 -0000 > On 3 Nov, 2015, at 18:22, Jeff Weeks wrote: >=20 > I believe that means 'count' has to reach some nearly impossibly high = value of (100ms/5198ns)^2 =3D=3D 370,107,128 >=20 > I say nearly impossible, because it will take minutes (hours?) to get = that high (if my math is correct, it'll take over 17 seconds just to = reach 7500). Note that since count increments on every signal given (every packet = dropped, in this case), it will increment faster as time goes on, as = long as there is a sufficient packet frequency to support it (as there = is in this case). However, even 17 seconds is obviously too slow to control the buffer. > In the meantime, the queue *isn't* being effectively managed, as = packets with extremely high latencies will be transmitted for far too = long. The problem is that you have an unresponsive flow here. Codel is = designed to give adequate congestion signals to *responsive* flows that = require only one signal per RTT. Unresponsive flows are instead caught = by the buffer limit, causing hard packet drops. This also means that where a responsive flow and an unresponsive flow = share the same buffer, Codel doesn=E2=80=99t perform very well; the = responsive flow backs off while the unresponsive flow continues to = saturate the buffer. (This is also what happens, intentionally, with = uTP and standard TCP in a dumb FIFO.) This is fixed if you combine Codel with flow isolation (ie. FQ), since = then the responsive and unresponsive flows do not share the same buffer. = When the buffer limit is reached, only the longest queue is culled, and = this will be the unresponsive flow. - Jonathan Morton