From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757253Ab2AXR52 (ORCPT ); Tue, 24 Jan 2012 12:57:28 -0500 Received: from g4t0017.houston.hp.com ([15.201.24.20]:40296 "EHLO g4t0017.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755244Ab2AXR51 (ORCPT ); Tue, 24 Jan 2012 12:57:27 -0500 Message-ID: <4F1EF104.1040107@hp.com> Date: Tue, 24 Jan 2012 09:57:24 -0800 From: Rick Jones User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.24) Gecko/20111109 Lightning/1.0b2 Thunderbird/3.1.16 MIME-Version: 1.0 To: leno soff CC: netdev@vger.kernel.org, linux-kernel@vger.kernel.org, eric.dumazet@gmail.com, davem@davemloft.net Subject: Re: How to accelerate tcp retransmition References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/24/2012 06:09 AM, leno soff wrote: > On Tue, Jan 24, 2012 at 4:58 PM, leno soff wrote: >> Hello everyone, >> I have a lot of client, say C1, C2, .. Cn, which route packets to >> my servers through router R. But R will drop 70% - 90% _ non-SYN _ >> packets from clients to Server. I think you should address that first - why does the router drop 70 to 905 of the non-SYN segments it receives. At first blush that sounds like a classic case of massive over-subscription, and any attempt to accelerate the retransmissions seems destined to trigger congestive collapse. As a side issue, if the router is dropping 70 to 90% of the non-SYN segments, why is it not also dropping 70 to 90% of the SYN segments? Also, I'm reasonably confident that an actual keepalive probe would not (or at least should not?) be considered in the three duplicate ACK heuristic. rick jones