From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.cs.ubc.ca (mail.cs.ubc.ca [142.103.6.71]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id ECA813CB43 for ; Thu, 22 Nov 2018 15:28:37 -0500 (EST) Received: from [198.162.52.72] (ventoux.cs.ubc.ca [198.162.52.72]) (authenticated bits=0) by mail.cs.ubc.ca (8.15.2/8.13.6) with ESMTPSA id wAMKSaq0007405 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO) for ; Thu, 22 Nov 2018 12:28:37 -0800 From: Fabian Ruffy To: cake@lists.bufferbloat.net Message-ID: <477d23a4-724c-2601-2cb2-ce1f0c0910f2@cs.ubc.ca> Date: Thu, 22 Nov 2018 12:28:36 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 Content-Type: text/html; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Mailman-Approved-At: Thu, 22 Nov 2018 16:04:07 -0500 Subject: [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 20:28:38 -0000

Hello,

this is a somewhat esoteric question. I am trying to actually force bufferbloat in an emulation setup I am using. I set up a dumbbell topology and push traffic through it, causing congestion at the central link. I use this setup to compare congestion avoidance algorithms such as DCTCP to other solutions.
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 is great, but in practice it prevents me from prototyping algorithms.

My interface configuration for bottlenecked links is:

qdisc tbf 5: dev OBcbnsw1-eth2 root refcnt 2 rate 10Mbit burst 15000b lat 12.0ms
Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
qdisc netem 10: dev OBcbnsw1-eth2 parent 5:1 limit 500
Sent 6042 bytes 51 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0

I have the suspicion that it is related to the CAKE changes in the 4.19 kernel, but I am not exactly sure. I am not using tc cake at all. Do you maybe know what could cause this behavior? Apologies if this is the wrong mailing list.

Thanks and best,

Fabian