From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jesper Dangaard Brouer Subject: Re: tc linklayer ADSL calc broken after commit 56b765b79 (htb: improved accuracy at high rates) Date: Thu, 30 May 2013 10:09:52 +0200 Message-ID: <20130530100952.032a4b61@redhat.com> References: <20130529151330.22c5c89e@redhat.com> <1369842724.5109.44.camel@edumazet-glaptop> <20130529155034.334092c5@nehalam.linuxnetplumber.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: Eric Dumazet , Jesper Dangaard Brouer , David Miller , j.vimal@gmail.com, Michal Soltys , Mike Frysinger , Jussi Kivilinna , Patrick McHardy , Jiri Pirko , Toke =?UTF-8?B?SMO4aWxhbmQtSsO4cmdlbnNl?= =?UTF-8?B?bg==?= , Dave Taht , netdev@vger.kernel.org, bloat@lists.bufferbloat.net, Dan Siemon , Jim Gettys , Steven Barth , Felix Fietkau , Jiri Benc , russell-tcatm@stuart.id.au To: Stephen Hemminger Return-path: Received: from mx1.redhat.com ([209.132.183.28]:7831 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967631Ab3E3IKs (ORCPT ); Thu, 30 May 2013 04:10:48 -0400 In-Reply-To: <20130529155034.334092c5@nehalam.linuxnetplumber.net> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 29 May 2013 15:50:34 -0700 Stephen Hemminger wrote: > On Wed, 29 May 2013 08:52:04 -0700 > Eric Dumazet wrote: > > > On Wed, 2013-05-29 at 15:13 +0200, Jesper Dangaard Brouer wrote: > > > I recently discovered that the (traffic control) tc linklayer > > > calculations for ATM/ADSL have been broken by: > > > commit 56b765b79 (htb: improved accuracy at high rates). > > > > > > Thus, people shaping on ADSL links, using e.g.: > > > tc class add ... htb rate X ceil Y linklayer atm overhead 10 > > > > > > Will no-longer get ATM cell tax/overhead adjusted. > > > > > > How can we solve/fix this? > > > Perhaps we can change to use the "stab" system instead (as it does > > > not seem to be broken by the commit). > > > > > > But how do we facilitate a change to use "stab" system (for all > > > the scripts using the old option)? > > > > > > Can we change the iproute2/tc command to handle this > > > transparently, or should we give an error/warning if someone uses > > > "tc" and "linklayer" on a kernel above v.3.8. ? > > > [...] > > How bad is the failure? If it is fixed, will it break existing > installations? There is no "failure", the ATM-aligned rate table send to the kernel is silently ignored. People using the linklayer ATM option will just be confused why their shaping scripts does not work, when situation of bufferbloat occurs. I guess that was why Dave Taht, was so confused, when he wanted to make his scripts DSL aware... > Which probably means, is anyone but the original developers ever > using it and therefore likely to notice? Me the "original developer" actually don't use as I don't have a ADSL line any-longer. I know of people using this. Dan Siemon have it as an option in his scripts (but uses VDSL with out ATM himself). I recently got contacted from someone in China, asking me to reconstruct my homepage: http://www.adsl-optimizer.dk/ as they were using it. The question is how do we fix this in a backward compatible manor? -- Best regards, Jesper Dangaard Brouer MSc.CS, Sr. Network Kernel Developer at Red Hat Author of http://www.iptv-analyzer.org LinkedIn: http://www.linkedin.com/in/brouer