netdev - Re: scp stalls mysteriously

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Date:	Sat, 05 Dec 2009 23:32:25 +0100
From:	Damian Lukowski <damian@....rwth-aachen.de>
To:	Frederic Leroy <fredo@...rox.org>
Cc:	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	Netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Greg KH <gregkh@...e.de>
Subject: Re: scp stalls mysteriously

Frederic Leroy schrieb:
> Le Thu, 03 Dec 2009 15:10:11 +0100,
> Damian Lukowski <damian@....rwth-aachen.de> a écrit :
>>> I suppose adding || !tp->retrans_stamp into the false condition is
>>> fine as long as we don't then have a connection that can cause a
>>> connection to hang there forever for some reason (this needs to be
>>> understood well enough, not just test driven in stables :-)).
>>>
>>>> Unluckily, I still cannot reproduce the scp stalls here, so it
>>>> would be nice if Frederic printed retrans_stamp together with
>>>> icsk_ca_state and icsk_retransmits, please.
>>> It wouldn't hurt to know tp->packets_out and tp->retrans_out too,
>>> that might have some significant w.r.t what happens because of FRTO.
>> I made a patch for Frederic with Codebase
>> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
>>
>> Thanks for testing.
> 
> I made a new .11 trace with damian patch.
> The copy went to the end.

Could you please make another test and unplug the cable or drop ACKs for
several seconds, so that some RTO retransmissions are performed?
I'd like to see if retrans_stamp remains constant. In the dmesg output of
the 11th run, it seems to change while icsk_retransmits also increases.
This is kind of bad for connection timeout calculation in the RTO case ...

Damian
 
> http://www.starox.org/pub/scp_stall/scp_stall-houba.11-patch_damian.pcap.bz2
> http://www.starox.org/pub/scp_stall/scp_stall-houba.11-patch_damian.dmesg.bz2
> http://www.starox.org/pub/scp_stall/scp_stall-houba.11-patch_damian.proc_net_netstat-before.bz2
> http://www.starox.org/pub/scp_stall/scp_stall-houba.11-patch_damian.proc_net_netstat-after.bz2
> http://www.starox.org/pub/scp_stall/scp_stall-houba.11-patch_damian.sysctl_net.ipv4.tcp-before.bz2

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