netdev - Re: [net-next PATCH v4 1/3] net: TCP thin-stream detection

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Message-id: <D40945A6-301D-485D-BB8C-826D2EB68DA4@nets.rwth-aachen.de>
Date:	Sun, 21 Feb 2010 12:23:55 +0100
From:	Alexander Zimmermann <zimmermann@...s.rwth-aachen.de>
To:	Pavel Machek <pavel@....cz>, Andreas Petlund <apetlund@...ula.no>,
	lars.eggert@...ia.com
Cc:	netdev@...r.kernel.org, Ilpo J?rvinen <ilpo.jarvinen@...sinki.fi>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Arnd Hannemann <Arnd.Hannemann@...s.rwth-aachen.de>,
	LKML <linux-kernel@...r.kernel.org>, shemminger@...tta.com,
	David Miller <davem@...emloft.net>,
	william.allen.simpson@...il.com,
	Lukowski Damian <damian@....rwth-aachen.de>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [net-next PATCH v4 1/3] net: TCP thin-stream detection


Am 21.02.2010 um 11:21 schrieb Pavel Machek:

> Hi!
> 
>> +After analysing a large number of time-dependent interactive
>> +applications, we have seen that they often produce thin streams
>> +and also stay with this traffic pattern throughout its entire
>> +lifespan. The combination of time-dependency and the fact that the
>> +streams provoke high latencies when using TCP is unfortunate.
>> +
>> +In order to reduce application-layer latency when packets are lost,
>> +a set of mechanisms has been made, which address these latency issues
>> +for thin streams. In short, if the kernel detects a thin stream,
>> +the retransmission mechanisms are modified in the following manner:
>> +
>> +1) If the stream is thin, fast retransmit on the first dupACK.
>> +2) If the stream is thin, do not apply exponential backoff.
> 
> 2) seems very dangerous/unfair. If network  congestion is caused just
> by thin streams, will the network just fall apart?

and 1) can also be dangerous if we have reordering on the path.

I strongly suggest that we discuss Andreas' idea on IETF TCPM *before*
we integrate it in the kernel and enable it for everyone

Alex,

as an netdev reader and TCPM member

> 
> 
> -- 
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//
// Dipl.-Inform. Alexander Zimmermann
// Department of Computer Science, Informatik 4
// RWTH Aachen University
// Ahornstr. 55, 52056 Aachen, Germany
// phone: (49-241) 80-21422, fax: (49-241) 80-22220
// email: zimmermann@...rwth-aachen.de
// web: http://www.umic-mesh.net
//

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