From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hagen Paul Pfeifer Subject: Re: 200 millisecond timeouts in TCP Date: Fri, 4 Jun 2010 01:10:02 +0200 Message-ID: <20100603231002.GG6914@nuttenaction> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Ivan Novick Return-path: Received: from alternativer.internetendpunkt.de ([88.198.24.89]:45779 "EHLO geheimer.internetendpunkt.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752675Ab0FCXKG (ORCPT ); Thu, 3 Jun 2010 19:10:06 -0400 Content-Disposition: inline In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: * Ivan Novick | 2010-06-03 15:37:24 [-0700]: >Using tcpdump and systemtap I am seeing that sometimes retransmission >of data is sent after waiting 200 milliseconds. However sometimes >retransmissions happen quicker. Quicker as 200ms? Conservatively the minimum TCP RTO should be 1s (rfc2988), Linux differs from this default and define the minimum RTO to 200ms: #define TCP_RTO_MIN ((unsigned)(HZ/5)) Can you post the tcpdump traces where the relevant retransmission is recognizable? >Also do you know if the timeout numbers for TCP are configurable parameters? Some values are documented in Documentation/networking/ip-sysctl.txt, you can find the relevant timer implementation in ipv4/tcp_input.c and the definition of TCP_RTO_MIN in include/net/tcp.h. Hagen Paul Pfeifer -- Hagen Paul Pfeifer || http://jauu.net/ Telephone: +49 174 5455209 || Key Id: 0x98350C22 Key Fingerprint: 490F 557B 6C48 6D7E 5706 2EA2 4A22 8D45 9835 0C22