From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Dumazet Subject: Re: [PATCH net-next v12 3/7] sch_cake: Add optional ACK filter Date: Thu, 17 May 2018 04:04:54 -0700 Message-ID: References: <152650253056.25701.10138252969621361651.stgit@alrua-kau> <152650254614.25701.1377066681230937234.stgit@alrua-kau> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Cc: cake@lists.bufferbloat.net To: =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , netdev@vger.kernel.org Return-path: Received: from mail-pf0-f193.google.com ([209.85.192.193]:45737 "EHLO mail-pf0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751274AbeEQLEz (ORCPT ); Thu, 17 May 2018 07:04:55 -0400 Received: by mail-pf0-f193.google.com with SMTP id c10-v6so1920953pfi.12 for ; Thu, 17 May 2018 04:04:55 -0700 (PDT) In-Reply-To: <152650254614.25701.1377066681230937234.stgit@alrua-kau> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 05/16/2018 01:29 PM, Toke Høiland-Jørgensen wrote: > The ACK filter is an optional feature of CAKE which is designed to improve > performance on links with very asymmetrical rate limits. On such links > (which are unfortunately quite prevalent, especially for DSL and cable > subscribers), the downstream throughput can be limited by the number of > ACKs capable of being transmitted in the *upstream* direction. > ... > > Signed-off-by: Toke Høiland-Jørgensen > --- > net/sched/sch_cake.c | 260 ++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 258 insertions(+), 2 deletions(-) > > I have decided to implement ACK compression in TCP stack itself. First step is to take care of SACK, which are the main source of the bloat, since we send one SACK for every incoming out-of-order packet. These SACK are not only causing pain on the network, they also cause the sender to send one MSS at a time (TSO auto defer is not engaged in this case), thus starting to fill its RTX queue with pathological skbs (1-MSS each), increasing processing time. I see that your ACK filter does not take care of this common case :) Doing the filtering in TCP has the immense advantage of knowing the RTT and thus be able to use heuristics causing less damage.