From mboxrd@z Thu Jan 1 00:00:00 1970 From: Markus Trippelsdorf Subject: Re: [PATCH net] net: fq_codel: Fix off-by-one error Date: Sat, 30 Mar 2013 16:08:52 +0100 Message-ID: <20130330150852.GA11315@x4> References: <1364514720-20780-1-git-send-email-subramanian.vijay@gmail.com> <1364569280.5113.21.camel@edumazet-glaptop> <20130330065345.GA23938@x4> <1364654567.5113.85.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Vijay Subramanian , netdev@vger.kernel.org, davem@davemloft.net To: Eric Dumazet Return-path: Received: from ud10.udmedia.de ([194.117.254.50]:50859 "EHLO mail.ud10.udmedia.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756589Ab3C3PIz (ORCPT ); Sat, 30 Mar 2013 11:08:55 -0400 Content-Disposition: inline In-Reply-To: <1364654567.5113.85.camel@edumazet-glaptop> Sender: netdev-owner@vger.kernel.org List-ID: On 2013.03.30 at 07:42 -0700, Eric Dumazet wrote: > On Sat, 2013-03-30 at 07:53 +0100, Markus Trippelsdorf wrote: > > On 2013.03.29 at 08:01 -0700, Eric Dumazet wrote: > > > > > > Just curious, did you play changing the default limit (10240 packets) ? > > > > I did some tests on my home router (running OpenWrt trunk) that is rate- > > limited with hfsc to the speed of the cable modem. > > > > My tests seem to indicate that lowering the default limit to 1024 > > packets results in much better latency behavior when using bittorrent. > > > > With the default limit (10240 packets) I would get huge ping latencies > > from 600-1200ms when downloading e.g.: > > http://download.opensuse.org/distribution/12.3/iso/openSUSE-12.3-DVD-x86_64.iso.torrent > > with hundreds of peers. > > > > Setting the limit to 1024 did get the latencies back in check (20-30ms > > with occasional spikes of ~100ms). > > Bittorent uses its own rate limiting technique, defeating > current cwnd control done in the TCP stack, because of a very known > problem > > ( http://www.ietf.org/id/draft-ietf-tcpm-newcwv-00.txt ) > > So if your goal is reducing latencies for a _given_ class of flows, just > use prio + 3 fq_codel, and classify your packets to make sure your > lovely ping packets are not dropped or behind long packets. This is exactly the setup that I'm using right now (prio + 4 fq_codel with bittorent set to low). And setting the fq_codel limit to 1024 improves latency in this situation. That's all I wanted to communicate. If the result doesn't interest you, just ignore my mail. -- Markus