From mboxrd@z Thu Jan 1 00:00:00 1970 From: John Heffner Subject: Re: TCP rx window autotuning harmful at LAN context Date: Wed, 11 Mar 2009 08:34:23 -0700 Message-ID: <1e41a3230903110834k7fd0e48clfb01e9ec5a189f1@mail.gmail.com> References: <20090309200505.GA58375@bts.sk> <20090309.170927.130334650.davem@davemloft.net> <87bps8fkaw.fsf@basil.nowhere.org> <20090311.063058.236235660.davem@davemloft.net> <20090311150149.GG11935@one.firstfloor.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: David Miller , md@bts.sk, netdev@vger.kernel.org To: Andi Kleen Return-path: Received: from qw-out-2122.google.com ([74.125.92.27]:17517 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752148AbZCKPe1 (ORCPT ); Wed, 11 Mar 2009 11:34:27 -0400 Received: by qw-out-2122.google.com with SMTP id 5so57723qwi.37 for ; Wed, 11 Mar 2009 08:34:24 -0700 (PDT) In-Reply-To: <20090311150149.GG11935@one.firstfloor.org> Sender: netdev-owner@vger.kernel.org List-ID: On Wed, Mar 11, 2009 at 8:01 AM, Andi Kleen wrote: > On Wed, Mar 11, 2009 at 06:30:58AM -0700, David Miller wrote: >> From: Andi Kleen >> Date: Wed, 11 Mar 2009 11:03:35 +0100 >> >> > Perhaps this points to the default buffer sizing heuristics to >> > be too aggressive for >= 1GB? >> >> It's necessary Andi, you can't fill a connection on a trans- >> continental connection without at least a 4MB receive buffer. > > Seems pretty arbitary to me. It's the value for a given bandwidth*latency > product, but why not half or twice the bandwidth? I don't think > that number is written in stone like you claim. It is of course just a number, though not exactly arbitrary -- it's approximately the required value for transcontinental 100 Mbps paths. Choosing the value is a matter of engineering trade-offs, and seemed like a reasonable cap at this time. Any cap so much lower that it would give a small bound for LAN latencies would bring us back to the bad old days where you couldn't get anything more than 10 Mbps on the wide area. -John