Xen users - Apr 2008 - Xen network latencies

Dear,

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?

- Joris

==
Configuration:
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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Hi Joris,

On Mon, Apr 21, 2008 at 6:00 AM, Joris Dobbelsteen <
joris@familiedobbelsteen.nl> wrote:
> Dear,
>
> 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,
Todd


[1] http://dast.nlanr.net/Projects/Iperf/
[2] http://xenoprof.sourceforge.net/
[3]
http://ieeexplore.ieee.org/Xplore/defdeny.jsp?url=/iel5/4299339/4299340/04299347.pdf&isnumber=4299340&prod=CNF&arnumber=4299347&arSt=2&ared=2&arAuthor=Apparao%2C+Padma%3B+Makineni%2C+Srihari%3B+Newell%2C+Don&code=2




>
> - Joris
>
> ==>
> Configuration:
> 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
> * ...?
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>

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Joris Dobbelsteen wrote:
> Dear,
> 
> 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?
Hi Joris,

I can''t recommend any way to measure the jitter but you may find a 
solution with a script called "wondershaper".

     http://lartc.org/wondershaper/

hth,
Mike Wright :m)

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