From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Heffner Subject: Re: TCP rx window autotuning harmful at LAN context Date: Mon, 9 Mar 2009 17:09:22 -0700 Message-ID: <1e41a3230903091709i740d95ddhefc1df2c71ea60b6@mail.gmail.com> References: <1e41a3230903091101u536a3b3bv7f0dd9da6891781e@mail.gmail.com> <20090309195906.M50328@bts.sk> <1e41a3230903091323j541d1895j2eb69b9f9c11f2f3@mail.gmail.com> <20090309.165205.11054081.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: md@bts.sk, netdev@vger.kernel.org To: David Miller Return-path: Received: from yx-out-2324.google.com ([74.125.44.28]:20979 "EHLO yx-out-2324.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752525AbZCJAJZ (ORCPT ); Mon, 9 Mar 2009 20:09:25 -0400 Received: by yx-out-2324.google.com with SMTP id 8so1253026yxm.1 for ; Mon, 09 Mar 2009 17:09:23 -0700 (PDT) In-Reply-To: <20090309.165205.11054081.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Mar 9, 2009 at 4:52 PM, David Miller wrote: > From: John Heffner > Date: Mon, 9 Mar 2009 13:23:15 -0700 > >> A drop-tail queue size of 1000 packets on a local interface is >> questionable, and I think this is the real source of your problem. > > Are you suggested we decrease it? :-) I am not so bold. :-D (And note the drop-tail prefix.) A long queue with AQM would probably be best, but would require careful testing before enabling by default. It would almost certainly cause pain for some. And, for the vast majority of people for whom the local interface is not the bottleneck, it makes no difference. It hurts worst for someone doing bulk transfer with a GigE device in 100 Mbps (or worse, 10-Mbps) mode, where 1000 pkts is a long time, while simultaneously doing something latency-sensitive. I suspect this is the case Marian is experiencing. -John