From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: TCP keepalive timer problem Date: Thu, 27 Aug 2009 16:29:27 +0200 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-Transfer-Encoding: QUOTED-PRINTABLE Cc: Andi Kleen , Li_Xin2@emc.com, linux-kernel@vger.kernel.org, netdev@vger.kernel.org To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <4A969566.3070606@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Thu, Aug 27, 2009 at 04:17:10PM +0200, Eric Dumazet wrote: > Andi Kleen a =E9crit : > > Eric Dumazet writes: > >> Now, 7200 seconds might be inappropriate for special needs, and co= nsidering > >> there is no way to change tcp_retries2 for a given socket (only ch= oice 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. > >=20 > > 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. > >=20 >=20 > tcp_retries2 is a number of retries, its difficult to derive a time f= rom it. That shouldn't be too hard.=20 >=20 > Also, it's not clear what behavior you are refering to. > Imagine we can be smart and compute tcp_retries2_time (in jiffies) fr= om tcp_retries2 > If keepalive_timer fires and we have packets in flight, what heuristi= c 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 =3D tcp_time_stamp - tp->rcv_tstamp; > ... >=20 > 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 (f= ollowing the RFC), but=20 still give expected behaviour to users who explicitely set short keepal= ives. -Andi --=20 ak@linux.intel.com -- Speaking for myself only.