netdev - Re: [PATCH v2 net] tcp: zero retrans_stamp if all retrans were acked

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Date:	Tue, 04 Nov 2014 17:20:45 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Marcelo Ricardo Leitner <mleitner@...hat.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	Netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH v2 net] tcp: zero retrans_stamp if all retrans were acked

On Tue, 2014-11-04 at 18:51 -0200, Marcelo Ricardo Leitner wrote:

> And thank you guys for all the assistance on it. Btw, would you send me that 
> packetdrill script? I'm curious to see how such corner case could be written 
> on it.

One of the script I saw was :

You might have to adapt preconditions (tcp_rmem[]/tcp_wmem[])

0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
// Set a 10s timeout
+.000 setsockopt(3, SOL_TCP, TCP_USER_TIMEOUT, [10000], 4) = 0
+.000 bind(3, ..., ...) = 0
+.000 listen(3, 1) = 0
+.000 < S 0:0(0) win 32792 <mss 1460,nop,wscale 7>
+.000 > S. 0:0(0) ack 1 <mss 1460,nop,wscale 6>
+.010 < . 1:1(0) ack 1 win 257
+.000 accept(3, ..., ...) = 4
+.000 write(4, ..., 1000) = 1000
+.000 > P. 1:1001(1000) ack 1
+.625 > P. 1:1001(1000) ack 1
+.020 < . 1:1(0) ack 1001 win 257
// Purposely write more after the specified timeout for testing
+11.0 write(4, ..., 1000) = 1000
+.000 > P. 1001:2001(1000) ack 1
+1.25 > P. 1001:2001(1000) ack 1
// socket is killed when the 2nd RTO fires at +2.50 w/o this patch
// so the next write returns ETIMEOUT
+2.60 write(4, ..., 1000) = 1000


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