netdev - Re: [PATCH] tcp: fix ICMP-RTO war

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Date:	Wed, 27 Jan 2010 14:36:18 +0200 (EET)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	Damian Lukowski <damian@....rwth-aachen.de>
cc:	Denys Fedoryshchenko <denys@...p.net.lb>,
	Netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Subject: Re: [PATCH] tcp: fix ICMP-RTO war

On Mon, 25 Jan 2010, Damian Lukowski wrote:

> considering Denys' latest tests, I think we should bound
> at TCP_RTO_MIN inside __tcp_set_rto().
> Look at the following piece:
> > [  604.193389] rto: 200 (0 >> 3 + 0, 32) time: 304193 sent: 304091 pen: 1 307291 rem: 98                                                                                         
> > [  604.193518] lower bound violation: 0 code 1 sk_state 1                                                                                                                        
> > [  604.193589] rto: 200 (0 >> 3 + 0, 31) time: 304193 sent: 304091 pen: 1 304291 rem: 98                                                                                         
> > [  604.193706] lower bound violation: 0 code 1 sk_state 1                                                                                                                        
> > [  604.193776] rto: 200 (0 >> 3 + 0, 30) time: 304193 sent: 304091 pen: 1 304291 rem: 98                                                                                         
> > [  607.341327] lower bound violation: 0 code 1 sk_state 1                                                                                                                        
> > [  607.341412] rto: 200 (0 >> 3 + 0, 33) time: 307341 sent: 307091 pen: 1 310291 rem: 0  
> 
> We have a burst of three incoming ICMPs, not triggering retransmissions because
> of rem > 0. Nevertheless, there is an increase of icsk_backoff by four
> within 3100ms, with no ICMPs in between.
> For me, this is explainable by the broken mdev/rtt issue together with
> bursty ICMP replies.

Unless they are for a different connection? We might have to print sk (%p) 
in all those printouts to be sure which maps to which. If a peer becomes 
unreachable, it may well have multiple connections open (this was a 
proxy, iirc?).

-- 
 i.
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