From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751542AbZH0OtF (ORCPT ); Thu, 27 Aug 2009 10:49:05 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751380AbZH0OtF (ORCPT ); Thu, 27 Aug 2009 10:49:05 -0400 Received: from gw1.cosmosbay.com ([212.99.114.194]:40959 "EHLO gw1.cosmosbay.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751139AbZH0OtE (ORCPT ); Thu, 27 Aug 2009 10:49:04 -0400 Message-ID: <4A969CDC.6060402@gmail.com> Date: Thu, 27 Aug 2009 16:49:00 +0200 From: Eric Dumazet User-Agent: Thunderbird 2.0.0.23 (Windows/20090812) MIME-Version: 1.0 To: Andi Kleen CC: Li_Xin2@emc.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org Subject: Re: TCP keepalive timer problem 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> <20090827142927.GA17220@basil.fritz.box> In-Reply-To: <20090827142927.GA17220@basil.fritz.box> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-1.6 (gw1.cosmosbay.com [0.0.0.0]); Thu, 27 Aug 2009 16:49:01 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andi Kleen a écrit : > 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. > Yep, so to recap we have two changes : 1) The one I sent (taking into account the time of last ACK we received) to compute the timer delays. 2) The one you suggest, avoiding to send a probe if we have packets in flight, relying on normal retransmits timers.