netdev - Re: [PATCH] tcp: fixing TLP's FIN recovery

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Date:	Mon, 09 Jun 2014 09:24:07 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Per Hurtig <per.hurtig@....se>
Cc:	Nandita Dukkipati <nanditad@...gle.com>,
	Netdev <netdev@...r.kernel.org>,
	Anna Brunström <anna.brunstrom@....se>,
	mohammad.rajiullah@....se, Neal Cardwell <ncardwell@...gle.com>,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
Subject: Re: [PATCH] tcp: fixing TLP's FIN recovery

On Mon, 2014-06-09 at 09:15 -0700, Eric Dumazet wrote:
> On Mon, 2014-06-09 at 17:56 +0200, Per Hurtig wrote:
> 
> > 
> > Ok, I guess you mean that the retransmission was not fast enough? But 
> > will the same not happen if the original FIN is not lost and triggers a 
> > SACK (i.e., if the two last data segments are still lost)?
> 
> Yes, I'd like to understand why Nandita specifically added the original
> test. In her tests, fast retransmit was not really effective.
> 
> Running packetdrill in a separate container gives me these interesting
> counters :
> 
> # nstat
> #kernel
> IpInReceives                    4                  0.0
> IpInDelivers                    4                  0.0
> IpOutRequests                   5                  0.0
> TcpPassiveOpens                 1                  0.0
> TcpInSegs                       4                  0.0
> TcpOutSegs                      10                 0.0
> TcpRetransSegs                  2                  0.0
> TcpExtTCPPureAcks               3                  0.0
> TcpExtTCPSackRecovery           1                  0.0
> TcpExtTCPFastRetrans            1                  0.0
> TcpExtTCPLossProbes             1                  0.0
> TcpExtTCPSackRecoveryFail       1                  0.0
> TcpExtTCPSackShiftFallback      1                  0.0
> TcpExtTCPRetransFail            4                  0.0   <<<< HERE >>>
> TcpExtTCPOrigDataSent           9                  0.0
> IpExtInOctets                   184                0.0
> IpExtOutOctets                  9212               0.0
> IpExtInNoECTPkts                4                  0.0
> 
> I guess we need to understand why the retransmit is in error.
> 
> I am investigating.
> 


Hmm... We hit this point... This is embarrassing I guess.

       if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk))
                return -EHOSTUNREACH; /* Routing failure or similar. */



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