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Re: [Xen-users] Xen network latencies

To: "Joris Dobbelsteen" <joris@xxxxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] Xen network latencies
From: "Todd Deshane" <deshantm@xxxxxxxxx>
Date: Mon, 21 Apr 2008 14:38:11 -0400
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Hi Joris,

On Mon, Apr 21, 2008 at 6:00 AM, Joris Dobbelsteen <joris@xxxxxxxxxxxxxxxxxxxxx> wrote:

I have a network that runs VoIP. It passes through an Xen box that has a firewall running as DomU. The VoIP traffic is very sensitive to jitter in arrival times. The jitter causes jerky audio. Its easy to reproduce by simply downloading a lot of data and saturating downstream bandwidth on the ADSL connection.

However I have a hard time figuring out the cause of the jitter, since my configuration is getting more complex at this point in time. So anyone has ideas how I can measure and determinate the cause of my problems? Maybe any solutions to this problem?

For a simple network benchmark tool, I would recommend iperf [1]. It is easy to use and can give you a sense of the bandwidth over time.

For a more low level look at potential problems with Xen you should consider taking a look at tools like xenoprof [2]

Characterization of network processing overheads in Xen [3] is an older paper on this topic, but could give you some hints and ideas on places to look. They use iperf and xenoprof, and are also developing a benchmark tool at Intel called vConsolidate.

Best Regards,

[1] http://dast.nlanr.net/Projects/Iperf/
[2] http://xenoprof.sourceforge.net/
[3] http://ieeexplore.ieee.org/Xplore/defdeny.jsp?url="">


- Joris


Network path:
* My ISP.
* Xen Dom0 receives.
* DomU firewall receives and sends.
* Xen Dom0 sends.
* VoIP box.

Xen 3.1.2 with Gentoo Linux 2.6.18 x86-64 on Dom0.
DomU is Debian Etch (4.0) x86-64 xen-linux.
Using default credit scheduler and having 12 domains at very low CPU usage (its a core 2 duo @ 2.0 GHz).

On the firewall DomU I already see lots of jitter.

Things to blame:
* My ISP (should not be)
* Xen scheduler
* Dom0 packet buffering
* DomU packet buffering
* Combination of the above
* ...?

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