From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752412AbZH0O3c (ORCPT ); Thu, 27 Aug 2009 10:29:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752241AbZH0O3c (ORCPT ); Thu, 27 Aug 2009 10:29:32 -0400 Received: from one.firstfloor.org ([213.235.205.2]:42300 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752155AbZH0O3a (ORCPT ); Thu, 27 Aug 2009 10:29:30 -0400 Date: Thu, 27 Aug 2009 16:29:27 +0200 From: Andi Kleen To: Eric Dumazet Cc: Andi Kleen , Li_Xin2@emc.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: TCP keepalive timer problem Message-ID: <20090827142927.GA17220@basil.fritz.box> References: <0939B589FC103041945B9F13274963E303B1A9D4@CORPUSMX90A.corp.emc.com> <4A93E36C.8070502@gmail.com> <0939B589FC103041945B9F13274963E303B1AD89@CORPUSMX90A.corp.emc.com> <4A967FCE.3000807@gmail.com> <87skfdl6qt.fsf@basil.nowhere.org> <4A969566.3070606@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <4A969566.3070606@gmail.com> User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 27, 2009 at 04:17:10PM +0200, Eric Dumazet wrote: > Andi Kleen a écrit : > > Eric Dumazet writes: > >> Now, 7200 seconds might be inappropriate for special needs, and considering > >> there is no way to change tcp_retries2 for a given socket (only choice being the global > >> tcp_retries2 setting), I would vote for a change in our stack, to *relax* RFC, > >> and get smaller keepalive timers if possible. > > > > I think the better fix would be to just to only do that when > > tcp_retries2 > keep alive time. So keep the existing behaviour > > with default keep alive, but switch when the user defined > > a very short keep alive. > > > > tcp_retries2 is a number of retries, its difficult to derive a time from it. That shouldn't be too hard. > > Also, it's not clear what behavior you are refering to. > Imagine we can be smart and compute tcp_retries2_time (in jiffies) from tcp_retries2 > If keepalive_timer fires and we have packets in flight, what heuristic do you suggest ? I didn't suggest to change something at firing time, just pattern the code you removed with if (keepalive_time > retries2 time) That's not perfect, but likely good enough. > if (tp->packets_out || tcp_send_head(sk)) > if (tcp_retries2_time < keepalive_time_when(tp)) > goto resched; > elapsed = tcp_time_stamp - tp->rcv_tstamp; > ... > > What would be the gain ? > Arming timer exactly every keepalive_time_when(tp) > instead of keepalive_time_when(tp) - (tcp_time_stamp - tp->rcv_tstamp) ? The gain would be that you don't send unnecessary packets by default (following the RFC), but still give expected behaviour to users who explicitely set short keepalives. -Andi -- ak@linux.intel.com -- Speaking for myself only.