From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marian =?utf-8?B?xI51cmtvdmnEjQ==?= Subject: Re: TCP rx window autotuning harmful at LAN context Date: Wed, 11 Mar 2009 09:29:20 +0100 Message-ID: <20090311082920.GA20543@bts.sk> References: <20090310114606.GA84964@bts.sk> <1e41a3230903100823h5d5768d9wb9f36eb294840814@mail.gmail.com> <20090310160040.GA93054@bts.sk> <20090310.091816.178102814.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Cc: johnwheffner@gmail.com, netdev@vger.kernel.org To: David Miller Return-path: Received: from saus.bts.sk ([194.160.23.4]:54025 "EHLO saus.bts.sk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750947AbZCKI3Y (ORCPT ); Wed, 11 Mar 2009 04:29:24 -0400 Content-Disposition: inline In-Reply-To: <20090310.091816.178102814.davem@davemloft.net> Sender: netdev-owner@vger.kernel.org List-ID: On Tue, Mar 10, 2009 at 09:18:16AM -0700, David Miller wrote: > There are both global system-wide and socket local limits to how much > memory can be consumed by TCP receive data. If things get beyond the > configured limits, we back off. You could modify those if you > personally wish. > > It's really good that you brought up this issue. > > And it's really good that you've explained your own personal > workaround for this issue. Beg your pardon - "personal" ?! Is our university the only place where people use Linux on workstations with 100 Mbps ethernet connection? Isn't the stock kernel supposed to work decently for them - or should they all become TCP experts and fiddle with various parameters in order not to cause harm to other applications or the whole LAN just by starting a single bulk transfer? For the last time: setting TCP window to BDP is well-known and generally accepted practice. Autotuning does NOT respect it, and for 100 Mpbs connections at LAN context it might set the rx window somewhere between 100*BDP and 300*BDP. Since the BDP formula obviously applies also in reverse direction, i.e. delay=window/bandwith setting insanely huge window results in insanely increased LAN latencies (upto buffer limits). Is this really something noone cares about ?!