From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: setsockopt() Date: Mon, 07 Jul 2008 15:50:21 -0700 Message-ID: <48729DAD.8010400@hp.com> References: <48725DFE.6000504@citi.umich.edu> <20080707142408.43aa2a2e@extreme> <48728B09.1050801@citi.umich.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: Stephen Hemminger , netdev@vger.kernel.org, Jim Rees , "J. Bruce Fields" To: Olga Kornievskaia Return-path: Received: from g4t0015.houston.hp.com ([15.201.24.18]:36427 "EHLO g4t0015.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755177AbYGGWuZ (ORCPT ); Mon, 7 Jul 2008 18:50:25 -0400 In-Reply-To: <48728B09.1050801@citi.umich.edu> Sender: netdev-owner@vger.kernel.org List-ID: Olga Kornievskaia wrote: > Stephen Hemminger wrote: >> It would be better if NFSD stayed out of doign setsockopt and just >> let the sender/receiver autotuning work? >> > > Auto-tuning would be guided by the sysctl values that are set for all > applications. I could be wrong but what I see is that unless an > application does a setsockopt(), its window is bound by the default > sysctl value. If it is true, than it is not acceptable. It means that in > order for NFSD to achieve a large enough window it needs to modify TCP's > sysctl value which will effect all other applications. My experience thusfar is that the sysctl defaults will allow an autotuned TCP receive window far larger than it will allow with a direct setsockopt() call. I'm still a triffle puzzled/concerned/confused by the extent to which autotuning will allow the receive window to grow, again based on some netperf experience thusfar, and patient explanations provided here and elsewhere, it seems as though autotuning will let things get to 2x what it thinks the sender's cwnd happens to be. So far under netperf testing that seems to be the case, and 99 times out of ten my netperf tests will have the window grow to the max. rick jones