From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-x642.google.com (mail-pl1-x642.google.com [IPv6:2607:f8b0:4864:20::642]) (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 6835E3CB43 for ; Thu, 22 Nov 2018 16:15:11 -0500 (EST) Received: by mail-pl1-x642.google.com with SMTP id e5so9693950plb.5 for ; Thu, 22 Nov 2018 13:15:11 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=networkplumber-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=1F7Ww8IhOaMFYLLO8wTXKfSzvMy4O56md7X4poXey8k=; b=fsDmXn11Gqfn6TSxRXQjMYTr+DbvOkceWst/l+qgn+y678TWnDPNaAAa4YxOJ/d+Dw PkCDuLCcRRcTwVsBUxbrKCVM1Id2o4QEWm8b7CQymI0ZM2y1MyMPgQ4xfxJ3yf8oPF8x bAP5JNTkN4KKMD2/Sd0+gZzPYCiSJwJV6WPIksSSs+8rA/XJz2EvJu5JfviAlvXLNceh e4QoXGXBJcQLtu3kpa8n17+PBlAt3iQ8WeMCXJNnf/iXV4HerXzBXmKi0JUJxxCy2cyc ZihhFsRW3ZSOWjyds8toqtESH9J9qB0qSrdHksm6tXIGomtqXG6RLsMZTYwFWwbQcz+N WJVQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=1F7Ww8IhOaMFYLLO8wTXKfSzvMy4O56md7X4poXey8k=; b=B1uV1gyljrWshDi9L+FNqwD2pOxKEV0n2mNVn5hGfAM2igNclTqK2RVhEdga/ML3VI 6EWGIailw/8p0xQY6asrCD66N2cIR+P40yAyL/WiQRzXH6KqHNgvfTXA4zONhrMVhrbG zKo6pDLorDR5pAhIXoL5l2vcSHlPlpQb6oEbJb46pg9i+Gpk99jmP85n9JWRKakbAH5E dIH2T59RqSElwwkzMaBFXn1zt5R2spnBZWBkT4xpz6Ed/e90IrljSCqa56e/786ogmEf jtclSu16JHMXQoWy1aoJFv8ydx/M3M+7fNw7BER8kfu6iLmHgI2cjU1Fubvv4HNLnXu5 jpsQ== X-Gm-Message-State: AA+aEWau6mDI4IYGFfVgYoEkkZK5StehnjYmNFkCK/2E3YxepOnBuiCQ jdaVfOElQPly/ZpO7B8bgNEu5BejJe8= X-Google-Smtp-Source: AFSGD/X5fz5QVK1JDhVYLYAYgeCSO8vduL6EQRG/NNYj73YrxleLjlU/645Cz/rFYIpUzNE/kDaPnA== X-Received: by 2002:a17:902:d03:: with SMTP id 3-v6mr12931999plu.66.1542921310473; Thu, 22 Nov 2018 13:15:10 -0800 (PST) Received: from xeon-e3 (204-195-22-127.wavecable.com. [204.195.22.127]) by smtp.gmail.com with ESMTPSA id f6sm25422666pfg.188.2018.11.22.13.15.09 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 22 Nov 2018 13:15:10 -0800 (PST) Date: Thu, 22 Nov 2018 13:15:08 -0800 From: Stephen Hemminger To: Fabian Ruffy Cc: cake@lists.bufferbloat.net Message-ID: <20181122131508.703f8b39@xeon-e3> In-Reply-To: <477d23a4-724c-2601-2cb2-ce1f0c0910f2@cs.ubc.ca> References: <477d23a4-724c-2601-2cb2-ce1f0c0910f2@cs.ubc.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [Cake] Emulating Bufferbloat 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: Thu, 22 Nov 2018 21:15:11 -0000 On Thu, 22 Nov 2018 12:28:36 -0800 Fabian Ruffy wrote: > Hello, >=20 > this is a somewhat esoteric question. I am trying to actually force buffe= rbloat in an emulation setup I am using. I set up a dumbbell topology and p= ush traffic through it, causing congestion at the central link. I use this = setup to compare congestion avoidance algorithms such as DCTCP to other sol= utions. > This has worked nicely with the 4.18 kernel. However, after upgrading to = 4.19 I cannot reproduce bufferbloat anymore. The traffic (even UDP packets)= is perfectly rate limited and I never see any congestion happening. This i= s great, but in practice it prevents me from prototyping algorithms. >=20 > My interface configuration for bottlenecked links is: >=20 > qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat= 12.0ms > > =C2=A0Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0) > > =C2=A0backlog 0b 0p requeues 0 > > qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500 > > =C2=A0Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0) > > =C2=A0backlog 0b 0p requeues 0 >=20 >=20 > I have the suspicion that it is related to the CAKE changes in the 4.19 k= ernel, but I am not exactly sure. I am not using tc cake at all. Do you may= be know what could cause this behavior? Apologies if this is the wrong mail= ing list. More likely it is a combination of TCP small queues and pacing support. To emulate a network you need to have an intermediate box, otherwise the lo= cal feedback in TCP will defeat what you are trying to do.