From: "J. Bruce Fields" Subject: Re: [PATCH 0/1] SUNRPC: Add sysctl variables for server TCP snd/rcv buffer values Date: Fri, 13 Jun 2008 16:56:20 -0400 Message-ID: <20080613205620.GN8501@fieldses.org> References: <484ECDE4.6030108@gmail.com> <7F44A14A-F811-4D41-BAFF-E019E9904B6A@oracle.com> <48518F18.2010703@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dean Hildebrand , linux-nfs@vger.kernel.org, aglo@citi.umich.edu To: Chuck Lever Return-path: Received: from mail.fieldses.org ([66.93.2.214]:57980 "EHLO fieldses.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753939AbYFMU4X (ORCPT ); Fri, 13 Jun 2008 16:56:23 -0400 In-Reply-To: Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Jun 13, 2008 at 02:51:18PM -0400, Chuck Lever wrote: > On Jun 12, 2008, at 5:03 PM, Dean Hildebrand wrote: >> I think the problem there is that the only way to set the buffer size >> automatically would be to know the rtt and bandwidth of the network >> connection. Excessive numbers of packets can get dropped if the TCP >> buffer is set too large for a specific network connection. > >> In this case, the window opens too wide and lets too many packets out >> into the system, somewhere along the path buffers start overflowing and >> packets are lost, TCP congestion avoidance kicks in and cuts the window >> size dramatically and performance along with it. This type of >> behaviour creates a sawtooth pattern for the TCP window, which is less >> favourable than a more steady state pattern that is created if the TCP >> buffer size is set appropriately. > > Agreed it is a performance problem, but I thought some of the newer TCP > congestion algorithms were specifically designed to address this by not > closing the window as aggressively. > > Once the window is wide open, then, it would appear that choosing a good > congestion avoidance algorithm is also important. Any references for Olga or I to read on that sort of behavior? --b.