From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-x22c.google.com (mail-lj1-x22c.google.com [IPv6:2a00:1450:4864:20::22c]) (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 D1AAA3BA8E for ; Fri, 30 Nov 2018 22:14:03 -0500 (EST) Received: by mail-lj1-x22c.google.com with SMTP id z80-v6so6691951ljb.8 for ; Fri, 30 Nov 2018 19:14:03 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=Y7q5Q/kjJSEa+0QXwPJQlDf9VyWapZkNXx8NDPE4+jU=; b=dHJZPsYtLQ8okR/ZsSTJqDiz3s0KdP/NfLBXJv9m2n/KjtEYfNAnvMPDHx+9oOFsnG uXMZECPJQ9vuiQaG0g2nRa+PfYHXZKeaVX1soK17u9az8AeLWx5fPP9dVXmEZXAHXJgS mquVi/qtGwyoE+yiqRAKKGYnZxTD/sI2J8eOzKIJ5dwEZiUqfvBmj/SYSlPpCrWBILtQ VNN5EmG+cQFcbqT17I4dRQuZ6hXOLyOoyX1k75zzK+MLU1svC1ZJp7i8bimf9t8Qksq1 1srzMn/PTlPmOeRyWLhsDvzDcpmRZIGUcNA6ol49V5qHm+m3UpMxdAq7nyP3fWfe++sl aejg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=Y7q5Q/kjJSEa+0QXwPJQlDf9VyWapZkNXx8NDPE4+jU=; b=aoU5QCMLYnmvWlWeBBPblLWYmJrxzMW4AYE6cXvK+ZesnjaImy5ys8thJIa9b/rTsj 5w+G/kcJnIJSriqkj5r26uW0RPkDwDo5EgdWmkXdB2kuJnH18iJbNcYyOOE33OExex6P rWZ2dZ5OYNYN838Guvf1L++3W9nTlzguXC8iexYzvJ5WPN02ke5yFalFvaXK0fQSGYx8 ECrNbPF43MvTsiAL31U0rImqkwX6p7cxCtDp6kbn/78MUKszb4pNULCGoVT1wx7uxYGA mFC1wSxX/3znxSNtLYlt6XiOpFQJX1LFpG9r0RN/q7NdINQXE+tvhUoKB40pcGJDSxTf BBvQ== X-Gm-Message-State: AA+aEWZY6HGw2slGfhyop+SuRsHOCnCRTg7H2jbrXrrBdqLMIWeTDaEN ET9KxDjQMEYUEm9Y2Smjxkc= X-Google-Smtp-Source: AFSGD/WPSLTtr01bzfG6gPnUfrt7Q4sF761Kg6lpaY/89wXZpkqNapSOAroMOzVVYtOSO/QRBenSZA== X-Received: by 2002:a2e:3509:: with SMTP id z9-v6mr5057708ljz.54.1543634042270; Fri, 30 Nov 2018 19:14:02 -0800 (PST) Received: from jonathartonsmbp.lan (83-245-236-220-nat-p.elisa-mobile.fi. [83.245.236.220]) by smtp.gmail.com with ESMTPSA id p10-v6sm1089527ljh.59.2018.11.30.19.14.01 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 30 Nov 2018 19:14:01 -0800 (PST) Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.1\)) Subject: Re: monitoring queue length From: Jonathan Morton In-Reply-To: Date: Sat, 1 Dec 2018 05:13:41 +0200 Cc: bloat-devel@lists.bufferbloat.net Content-Transfer-Encoding: quoted-printable Message-Id: <3D0D58C0-B601-413B-B3EA-80C396E6187B@gmail.com> References: To: Azin Neishaboori X-Mailer: Apple Mail (2.3445.9.1) X-BeenThere: bloat-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: "Developers working on AQM, device drivers, and networking stacks" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 01 Dec 2018 03:14:04 -0000 > On 1 Dec, 2018, at 12:05 am, Azin Neishaboori = wrote: >=20 > I do not know if this backlog is indeed queue length or not. It seems = strange to be queue length, because even when I flood the network with = high UDP data rates over capacity, it still shows 0b of backlog. Am I = looking at the wrong parameter? If so, could you please point out the = tool that shows the instantaneous queue length? There are two potential points of confusion here: 1: Linux throttles both TCP and UDP at the application socket level to = prevent queues building up in the qdiscs and HW devices. If it's your = machine producing the packets, that's probably the effect you're seeing; = there'll be a few packets queued in the HW (invisibly) and none in the = qdisc. That's approximately true regardless of which qdisc is in use, = though with a shaping qdisc you might see a few packets collect there = instead of in the HW. 2: If your traffic is coming from outside, it won't be queued upon = receipt unless you introduce an artificial bottleneck. There are ways = of doing that. For queuing experiments, we normally set up a "dumbbell" topology in = which two different machines act as source and drain of traffic, and a = third machine in the middle acts as a network emulator with artificial = delays, losses and bandwidth limits. That middlebox is where you would = then observe the queuing. - Jonathan Morton