Messages in this thread | | | Date | Thu, 27 Aug 2009 16:49:00 +0200 | From | Eric Dumazet <> | Subject | Re: TCP keepalive timer problem |
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Andi Kleen a écrit : > On Thu, Aug 27, 2009 at 04:17:10PM +0200, Eric Dumazet wrote: >> Andi Kleen a écrit : >>> Eric Dumazet <eric.dumazet@gmail.com> 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.
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