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

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Message-ID: <1402324756.3645.362.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 09 Jun 2014 07:39:16 -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 07:33 -0700, Eric Dumazet wrote:
> On Mon, 2014-06-09 at 15:13 +0200, Per Hurtig wrote:
> > >
> > Yes, it needs a SACK that covers one "sequence number", which a FIN
> > does. I don't see why it shouldn't generate a SACK? See below for some 
> > packet dumps.
> 
> I cooked following packetdrill test :
> 
> $ cat tlp-10pkt-fin.pkt 
> `../common/defaults.sh`
> // Establish a connection.
> 0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
> 0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
> 0.000 bind(3, ..., ...) = 0
> 0.000 listen(3, 1) = 0
> 
> 0.100 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
> 0.100 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6>
> 0.200 < . 1:1(0) ack 1 win 257
> 0.200 accept(3, ..., ...) = 4
> 
> // Send 8 MSS.
> 0.200 write(4, ..., 8000) = 8000
> +.000 > P. 1:8001(8000) ack 1
> +.000   close(4) = 0
> +.000 > F. 8001:8001(0) ack 1
> 
> // Receiver ACKs 7 packets
> 0.300 < . 1:1(0) ack 7001 win 257
> // check if TLP re-sends the FIN
> 0.500 > F. 8001:8001(0) ack 1
> 0.600 < . 1:1(0) ack 7001 win 257 <sack 8001:8001,nop,nop>
> // check if fast restransmit is correctly triggered.
> 0.600 > P. 7001:8001(1000) ack 1
> 
> # ../packetdrill tlp-10pkt-fin.pkt
> tlp-10pkt-fin.pkt:26: error handling packet: timing error: expected
> outbound packet at 0.600000 sec but happened at 1.099761 sec
> script packet:  0.600000 P. 7001:8001(1000) ack 1 
> actual packet:  1.099761 P. 7001:8001(1000) ack 1 win 457 
> 
> So it looks like fast retransmit is not triggered.
> 

And using instead :

# cat tlp-10pkt-fin.pkt
// Set up production config.
`../common/defaults.sh`

// Establish a connection.
0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
0.000 bind(3, ..., ...) = 0
0.000 listen(3, 1) = 0

0.100 < S 0:0(0) win 32792 <mss 1000,sackOK,nop,nop,nop,wscale 7>
0.100 > S. 0:0(0) ack 1 <mss 1460,nop,nop,sackOK,nop,wscale 6>
0.200 < . 1:1(0) ack 1 win 257
0.200 accept(3, ..., ...) = 4

// Send 8 MSS.
0.200 write(4, ..., 8000) = 8000
+.000 > P. 1:8001(8000) ack 1
+.000   close(4) = 0
+.000 > F. 8001:8001(0) ack 1

// Receiver ACKs 7 packets
0.300 < . 1:1(0) ack 7001 win 257

0.500 > F. 8001:8001(0) ack 1
0.600 < . 1:1(0) ack 7001 win 257 <sack 8001:8002,nop,nop>
0.600 > P. 7001:8001(1000) ack 1

# ../packetdrill tlp-10pkt-fin.pkt
tlp-10pkt-fin.pkt:26: error handling packet: timing error: expected
outbound packet at 0.600000 sec but happened at 0.624721 sec
script packet:  0.600000 P. 7001:8001(1000) ack 1 
actual packet:  0.624721 P. 7001:8001(1000) ack 1 win 457 




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