netdev - Re: [PATCH][v4] tcp: fix ICMP-RTO war

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Date:	Sun, 21 Feb 2010 18:10:29 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ilpo.jarvinen@...sinki.fi
Cc:	damian@....rwth-aachen.de, netdev@...r.kernel.org
Subject: Re: [PATCH][v4] tcp: fix ICMP-RTO war

From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Date: Tue, 16 Feb 2010 14:45:25 +0200 (EET)

> On Wed, 10 Feb 2010, Damian Lukowski wrote:
> 
>> @@ -5783,12 +5783,10 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
>>  
>>  				/* tcp_ack considers this ACK as duplicate
>>  				 * and does not calculate rtt.
>> -				 * Fix it at least with timestamps.
>> +				 * Force it here.
>>  				 */
>> -				if (tp->rx_opt.saw_tstamp &&
>> -				    tp->rx_opt.rcv_tsecr && !tp->srtt)
>> -					tcp_ack_saw_tstamp(sk, 0);
>> -
>> +				tcp_ack_update_rtt(sk, 0, 0);
>> +
> 
> ...Here a zero seq_rtt is given to RTT estimator (it will be effective 
> only in the case w/o timestamps, TS case recalculates it from the stored 
> timestamps). Maybe we could use some field (timestamp related one comes to 
> my mind) in request sock to get a real RTT estimate for non-timestamp case 
> too. ...It seems possible to me, though tricky because the request_sock is 
> no longer that easily available here so some parameter passing would be 
> needed.

Agreed.

But even more simply I think we should make even the current
tcp_ack_update_rtt() call here conditional on at least
tp->srtt being zero.

Damian do you at least agree with that?
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