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Message-ID: <alpine.DEB.2.00.1106211423400.17529@wel-95.cs.helsinki.fi>
Date: Tue, 21 Jun 2011 14:25:20 +0300 (EEST)
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To: Alexander Zimmermann <zimmermann@...s.rwth-aachen.de>
cc: Dominik Kaspar <dokaspar.ietf@...il.com>,
Carsten Wolff <carsten@...ffcarsten.de>,
John Heffner <johnwheffner@...il.com>,
Eric Dumazet <eric.dumazet@...il.com>,
Netdev <netdev@...r.kernel.org>,
Lennart Schulte <Lennart.Schulte@...sys.rwth-aachen.de>,
Arnd Hannemann <arnd@...dnet.de>
Subject: Re: Linux TCP's Robustness to Multipath Packet Reordering
On Wed, 27 Apr 2011, Alexander Zimmermann wrote:
> Hi,
>
> Am 27.04.2011 um 18:22 schrieb Dominik Kaspar:
>
> > Hi Carsten,
> >
> > Thanks for your feedback. I made some new tests with the same setup of
> > packet-based forwarding over two emulated paths (600 KB/s, 10 ms) +
> > (400 KB/s, 100 ms). In the first experiments, which showed a step-wise
> > adaptation to reordering, SACK, DSACK, and Timestamps were all
> > enabled. In the experiments, I individually disabled these three
> > mechanisms and saw the following:
> >
> > - Disabling timestamps causes TCP to never adjust to reordering at all.
>
> Reordering detection with DSACK is broken in Linux. We will fix that in
> a couple of weeks...
>
> > - Disabling SACK allows TCP to adapt very rapidly ("perfect" aggregation!).
>
> If you disable SACK, you will use the NewReno detection
Which probably has some reordering over-estimate bugs on its own...
(but I've forgotten details of my suspicion long time ago so please don't
ask for the them).
--
i.
--
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