From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: TCP funny-ness when over-driving a 1Gbps link. Date: Thu, 19 May 2011 17:37:07 -0700 Message-ID: <4DD5B7B3.2000505@candelatech.com> References: <4DD59DF2.2070707@candelatech.com> <20110519161827.2ba4b40e@nehalam> <4DD5A5CD.7040303@candelatech.com> <4DD5AAFC.8070509@candelatech.com> <1305849940.8149.1122.camel@tardy> <4DD5B202.7080701@candelatech.com> <1305851079.8149.1127.camel@tardy> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Stephen Hemminger , netdev To: rick.jones2@hp.com Return-path: Received: from mail.candelatech.com ([208.74.158.172]:48492 "EHLO ns3.lanforge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932665Ab1ETAhJ (ORCPT ); Thu, 19 May 2011 20:37:09 -0400 In-Reply-To: <1305851079.8149.1127.camel@tardy> Sender: netdev-owner@vger.kernel.org List-ID: On 05/19/2011 05:24 PM, Rick Jones wrote: >>>> [root@i7-965-1 igb]# netstat -an|grep tcp|grep 8.1.1 >>>> tcp 0 0 8.1.1.1:33038 0.0.0.0:* LISTEN >>>> tcp 0 0 8.1.1.1:33040 0.0.0.0:* LISTEN >>>> tcp 0 0 8.1.1.1:33042 0.0.0.0:* LISTEN >>>> tcp 0 9328612 8.1.1.2:33039 8.1.1.1:33040 ESTABLISHED >>>> tcp 0 17083176 8.1.1.1:33038 8.1.1.2:33037 ESTABLISHED >>>> tcp 0 9437340 8.1.1.2:33037 8.1.1.1:33038 ESTABLISHED >>>> tcp 0 17024620 8.1.1.1:33040 8.1.1.2:33039 ESTABLISHED >>>> tcp 0 19557040 8.1.1.1:33042 8.1.1.2:33041 ESTABLISHED >>>> tcp 0 9416600 8.1.1.2:33041 8.1.1.1:33042 ESTABLISHED >>> >>> I take it your system has higher values for the tcp_wmem value: >>> >>> net.ipv4.tcp_wmem = 4096 16384 4194304 >> >> Yes: >> [root@i7-965-1 igb]# cat /proc/sys/net/ipv4/tcp_wmem >> 4096 16384 50000000 > > Why?!? Are you trying to get link-rate to Mars or something? (I assume > tcp_rmem is similarly set...) If you are indeed doing one 1 GbE, and no > more than 100ms then the default (?) of 4194304 should have been more > than sufficient. Well, we occasionally do tests over emulated links that have several seconds of delay and may be running multiple Gbps. Either way, I'd hope that offering extra RAM to a subsystem wouldn't cause it to go nuts. Assuming this isn't some magical 1Gbps issue, you could probably hit the same problem with a wifi link and default tcp_wmem settings... >>> and whatever is creating the TCP connections is not making explicit >>> setsockopt() calls to set SO_*BUF. >> >> It is configured not to, but if you know of an independent way to verify >> that, I'm interested. > > You could always strace the code. Yeah...might be easier in this case to just comment out all those calls and do a quick test. Will be tomorrow before I can get to that, however.. Thanks, Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com