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Message-ID: <20090615160254.GA8550@rivendell>
Date: Mon, 15 Jun 2009 18:02:54 +0200
From: Raphael Hertzog <raphael@...za.com>
To: Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>
Cc: Netdev <netdev@...r.kernel.org>
Subject: Re: Constantly varying download rate with a complex xen networking
setup, why?
Le lundi 15 juin 2009, Ilpo Järvinen a écrit :
> On Mon, 15 Jun 2009, Raphael Hertzog wrote:
>
> > My problem is that when I download a big file from the internet by HTTP in
> > the dom0, the download rate is not stable. It goes up progressively and then
> > stalls for a few seconds, and restart again going up progressively (and
> > all this in loop until the download is complete).
>
> My guess: TCP sawtooth pattern and the associated loss recovery...? What
> you describe here seems to match exactly to what is expected to happen
> because of it (I see this happening quite often actually).
Why would this not happen for the same transfer done through a proxy (that
runs on the same machine but different domU)?
> What is the size of the bottleneck buffer and base RTTs of the relevant
> flows (HTTP, ssh)?
How can I collect those information?
> Please verify "blocking" using tcpdump or so. You may find out e.g. that
I'll try to do so and follow-up.
> network is not stalled but that out-of-order arrivals prevent
> applications from making progress.
>
> If this matches with your problem, deploying AQM at the bottleneck would
> help.
The bottleneck in my test setup is the ADSL connection and I don't control
the ADSL router.
Cheers,
--
Raphaël Hertzog -+- http://www.ouaza.com
Freexian : des développeurs Debian au service des entreprises
http://www.freexian.com
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