Subject: Re: Constantly varying download rate with a complex xen networking setup, why?

From: Raphael Hertzog <[email-masked]>
Date: Mon, 15 Jun 2009 18:02:54 +0200

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

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