netdev - Re: TCP keepalive timer problem

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Date:	Fri, 28 Aug 2009 09:05:44 +0200
From:	Damian Lukowski <damian@....rwth-aachen.de>
To:	Li_Xin2@....com
Cc:	eric.dumazet@...il.com, andi@...stfloor.org, netdev@...r.kernel.org
Subject: Re: TCP keepalive timer problem

Li_Xin2@....com schrieb:
>  > 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.
> 
> I agree with these two changes, but I think the patch for point 2 given
> by Eric is not correct:
> 
> 
> elapsed = keepalive_time_when(tp);
> 
>  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;

Hello,
I didn't follow the conversation in all details, but I submitted a series of
patches recently, in which one of those the time was calculated out of
tcp_retries. It's the post "[PATCH 3/3] Revert Backoff [v3]: Calculate TCP's
connection close threshold as a time value." from Aug 26, 2009 at 12:16 CEST.

This is the code with the calculation procedure:

--
> static inline bool retransmits_timed_out(const struct sock *sk,
> 					 unsigned int boundary)
> {
> 	int limit, K;
> 	if (!inet_csk(sk)->icsk_retransmits)
> 		return false;
> 
> 	K = ilog2(TCP_RTO_MAX/TCP_RTO_MIN);
> 
> 	if (boundary <= K)
> 		limit = ((2 << boundary) - 1) * TCP_RTO_MIN;
> 	else
> 		limit = ((2 << K) - 1) * TCP_RTO_MIN +
> 			(boundary - K) * TCP_RTO_MAX;
> 
> 	return (tcp_time_stamp - tcp_sk(sk)->retrans_stamp) >= limit;
> }
--

Given some boundary like tcp_retries2, it computes a limit, which should
be your tcp_retries2_time.
If that's not what you meant, then I'm sorry, and you can ignore it. :)

Regards
--
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