From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stephen Hemminger Subject: Re: [PATCH] tcp: make TCP quick ACK behavior modifiable Date: Mon, 23 Aug 2010 12:14:49 -0700 Message-ID: <20100823121449.29419771@nehalam> References: <1282590037-18566-1-git-send-email-hagen@jauu.net> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: netdev@vger.kernel.org, "David S. Miller" , Eric Dumazet , Ilpo =?ISO-8859-1?B?SuRydmluZW4=?= To: Hagen Paul Pfeifer Return-path: Received: from mail.vyatta.com ([76.74.103.46]:41688 "EHLO mail.vyatta.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754223Ab0HWTOw (ORCPT ); Mon, 23 Aug 2010 15:14:52 -0400 In-Reply-To: <1282590037-18566-1-git-send-email-hagen@jauu.net> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, 23 Aug 2010 21:00:37 +0200 Hagen Paul Pfeifer wrote: > The TCP quick ACK mechanism analyze if a connection is interactive or > not. Per default the quick ACK mechanism is enabled and ACK packets are > triggered instantly to raise the CWND fast - which is clever for > bulk data (non-interactive) flows. On the other hand interactive protocols > like HTTP, SMTP or XMPP will suffer from the quick ACK mechanism > because one additional packets is generated. A simple heuristic > detects if a connection is interactive (pingpong) and if so, > disable the quick ACK. But, the mechanism is not in the ability to > blindly guess if a connection is interactive, and so it must wait for at > least one return packet with payload. > > For the server side this requires one additional packet because (packet > number 5 and 6 can be combined): > > 192.168.1.35.44833 > 78.47.222.210.80: Flags [S], seq 2854340018, win 5840, options [mss 1460,sackOK,TS val 4382726 ecr 0,nop,wscale 7], length 0 > 78.47.222.210.80 > 192.168.1.35.44833: Flags [S.], seq 719041385, ack 2854340019, win 5792, options [mss 1452,sackOK,TS val 2606891996 ecr 4382726,nop,wscale 7], length 0 > 192.168.1.35.44833 > 78.47.222.210.80: Flags [.], ack 1, win 46, options [nop,nop,TS val 4382730 ecr 2606891996], length 0 > 192.168.1.35.44833 > 78.47.222.210.80: Flags [P.], seq 1:682, ack 1, win 46, options [nop,nop,TS val 4382730 ecr 2606891996], length 681 > 78.47.222.210.80 > 192.168.1.35.44833: Flags [.], ack 682, win 56, options [nop,nop,TS val 2606892002 ecr 4382730], length 0 > 78.47.222.210.80 > 192.168.1.35.44833: Flags [.], seq 1:1441, ack 682, win 56, options [nop,nop,TS val 2606892002 ecr 4382730], length 1440 > 192.168.1.35.44833 > 78.47.222.210.80: Flags [.], ack 1441, win 69, options [nop,nop,TS val 4382737 ecr 2606892002], length 0 > > This patch provides a sysctl interface for the administrator to globally > enable or disable TCP quick ACKs. Short lived protocols like HTTP will > save a non unimportant portion of packets! If this is configurable (still not sure about having yet more TCP knobs). It should either be per-socket or a route metric so it can be controlled on a per-path basis. --