netdev - Re: TCP connection stalls under 2.6.24.7

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Date:	Fri, 18 Jul 2008 11:14:51 +0200
From:	Thomas Jarosch <thomas.jarosch@...ra2net.com>
To:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Cc:	Jozsef Kadlecsik <kadlec@...ckhole.kfki.hu>,
	Netdev <netdev@...r.kernel.org>,
	Patrick McHardy <kaber@...sh.net>,
	Sven Riedel <sr@...urenet.de>,
	Netfilter Developer Mailing List 
	<netfilter-devel@...r.kernel.org>,
	"Dâniel Fraga" <fragabr@...il.com>,
	David Miller <davem@...emloft.net>
Subject: Re: TCP connection stalls under 2.6.24.7

Moi Ilpo,

On Thursday, 17. July 2008 17:53:01 Ilpo Järvinen wrote:
> > > One option would be to disable reentry to FRTO when some progress was
> > > made... Please try with the patch below...
>
> Ah, I just forgot that the situation might persist... Try with this
> one instead...

Good news everyone: Two connections made it to the finish line.

The bad part: One transfer took four minutes, the other sixteen minutes.
A colleague commented it's still much faster than carrying the message
by plane ;-) A session without FRTO takes around 84 seconds.

I've added debug printks() to every return path in tcp_use_frto(),
so you can see what's going on. They look like this:

Jul 18 10:20:40 intratest131 kernel: [  957.318006] tcp_use_frto: ENTER: frto_counter: 0, icsk->icsk_ca_state: 0
Jul 18 10:20:40 intratest131 kernel: [  957.318011] tcp_use_frto: DEFAULT RETURN 1;
Jul 18 10:21:08 intratest131 kernel: [  984.446006] tcp_use_frto: ENTER: frto_counter: 3, icsk->icsk_ca_state: 0
Jul 18 10:21:08 intratest131 kernel: [  984.446011] tcp_use_frto: RETURN in "tp->frto_counter > 1 || icsk->icsk_ca_state == TCP_CA_Loss"
Jul 18 10:21:14 intratest131 kernel: [  991.058006] tcp_use_frto: ENTER: frto_counter: 0, icsk->icsk_ca_state: 0
Jul 18 10:21:14 intratest131 kernel: [  991.058011] tcp_use_frto: DEFAULT RETURN 1;

Here are two new dumps and the corresponding debug traces:
http://www.intra2net.com/de/download/tcpdump/tcp_frto_second_patch.tar.bz2

Enjoy,
Thomas
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