From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Hutchings Subject: Re: TCP not triggering a fast retransmit? Date: Thu, 01 Jul 2010 02:23:53 +0100 Message-ID: <1277947433.4878.11.camel@localhost> References: <1277931829.4878.9.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, jmatthews@greenplum.com, Tim Heath , Herbert Xu To: Ivan Novick Return-path: Received: from mail.solarflare.com ([216.237.3.220]:47428 "EHLO exchange.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914Ab0GABX6 (ORCPT ); Wed, 30 Jun 2010 21:23:58 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On Wed, 2010-06-30 at 17:27 -0700, Ivan Novick wrote: > On Wed, Jun 30, 2010 at 2:03 PM, Ben Hutchings > wrote: > > On Wed, 2010-06-30 at 11:04 -0700, Ivan Novick wrote: > >> Hello all, > >> > >> Attached is a packet capture from my application that is running on > >> RedHat Enterprise Linux 5.4 > >> > >> I am seeing a Retransmission timeout but I was hoping this case would > >> go into fast retransmit and not RTO. > >> > >> I am wondering why did the sender not send more data? If the sender > >> was to send more data and extend the window then it would seem the > >> duplicate acks or SACKS should trigger fast retransmit. > > [...] > > > > In that packet capture I see TCP payload lengths which are 2, 3 and 4 > > times the usual MSS of 1448 bytes, which implies that GRO or LRO is in > > use. In RHEL 5.4 the TCP stack does not ACK often enough in this case > > because it is missing this change: > > > > commit ff9b5e0f08cb650d113eef0c654f931c0a7ae730 > > Author: Herbert Xu > > Date: Thu Aug 31 15:11:02 2006 -0700 > > > > [TCP]: Fix rcv mss estimate for LRO > > Wow, Thanks! Is this the patch you are talking about: > http://www.mail-archive.com/netdev@vger.kernel.org/msg21151.html ? > > It looks like a one liner. I could apply it and rebuild my RHEL 5.4 > to see if it helps. Right, that's the same patch. Ben. -- Ben Hutchings, Senior Software Engineer, Solarflare Communications Not speaking for my employer; that's the marketing department's job. They asked us to note that Solarflare product names are trademarked.