From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from iramx2.ira.uni-karlsruhe.de (iramx2.ira.uni-karlsruhe.de [141.3.10.81]) (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 D58CA3BA8E for ; Tue, 5 Jun 2018 07:01:58 -0400 (EDT) Received: from i72t450mh.tm.uni-karlsruhe.de ([141.3.71.47]) by iramx2.ira.uni-karlsruhe.de with esmtpsa port 587 iface 141.3.10.81 id 1fQ9iv-00016C-OH; Tue, 05 Jun 2018 13:01:57 +0200 To: Jonathan Morton Cc: bloat@lists.bufferbloat.net References: <152717340941.28154.812883711295847116.malone@soybean.canonical.com> <4f67f9b3-05a1-8d15-0aee-dfe8ea730d7c@gmail.com> <73c25a21-0ace-b5ee-090e-d06fb3b8dc60@kit.edu> <5CCC459D-A142-42F9-BD10-97E69ED7E8F3@gmail.com> From: Mario Hock Message-ID: Date: Tue, 5 Jun 2018 13:01:57 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <5CCC459D-A142-42F9-BD10-97E69ED7E8F3@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ATIS-AV: ClamAV (iramx2.ira.uni-karlsruhe.de) X-ATIS-Timestamp: iramx2.ira.uni-karlsruhe.de esmtpsa 1528196517.810057727 Subject: Re: [Bloat] Fwd: [Bug 1436945] Re: devel: consider fq_codel as the default qdisc for networking X-BeenThere: bloat@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: General list for discussing Bufferbloat List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 05 Jun 2018 11:01:59 -0000 Am 05.06.2018 um 09:49 schrieb Jonathan Morton: >> On 5 Jun, 2018, at 10:44 am, Mario Hock wrote: >> >> Just to make sure that I got your answer correctly. The benefit for endsystems comes from the "fq" (flow queuing) part, not from the "codel" part of fq_codel? > > That's a fair characterisation, yes. > > In fact, even for middleboxes, the "flow isolation" semantics of FQ have the most impact on reducing inter-flow induced latency. The "codel" part (AQM) helps with intra-flow latency, which is usually much less important once flow isolation is in place, but is still worth having. Thanks for the confirmation. A potential drawback of using the codel part (of fq_codel) in the endsystems is that it can cause packet drops already at the sender. I could actually confirm this assumption with a very simple experiment consisting of two servers connected over a 1Gbit/s link and 100 parallel flows (iperf3). With fq_codel I had 5,000-10,000 retransmissions within 60s. With fq (or pfifo_fast) no packets are dropped. (I presume either "TCP small queues" or backpressure keeps the queues from overflowing.) Also, ping times (delays for short flows) were similar with fq and fq_codel (mostly <= 1ms). Is there any advantage of using fq_codel over fq at the endsystems? Mario Hock