[Xen-users] Re: [Bridge] Performance and limitations of virtual bridges

[Stephen Hemminger <shemminger@xxxxxxxxxxxxxxxxxxxx>]

On Mon, 7 May 2007 20:32:17 +0200
Fermín Galán Márquez <fermin.galan@xxxxxxx> wrote:

> Hi,
> 
> Is there a limit in the number of interfaces a virtual bridge (created with
> brctl) can support without having a severe impact in performance?

The problem with lots of interfaces is that if destination address is not
known (or multicast/broadcast) the packet has to be copied and sent N times.

> I guess that there is no absolute answer for that question :), but maybe
> there is some kind of procedure/tool to know the "stress" or "load" that a
> virtual bridge is supporting in a given moment (in a similar way that a
> "top" can show you the CPU load).

Worst case is the flooding problem.

> My question is due to I'm using a virtual bridge with 14 interfaces (each
> interface correspond to a Xen virtual machine in the same physical host)
> and, given that I'm experiencing transmission delays in the network
> supported by the bridge, I'm suspecting about a loss of performance of it.

Probably when flooding it has to wake up all the guest machines and
that is sucking your performance on hypervisor switches.

> Thanks in advance!
> 
> Best regards,
> 
> --------------------
> Fermín Galán Márquez
> CTTC - Centre Tecnològic de Telecomunicacions de Catalunya
> Parc Mediterrani de la Tecnologia, Av. del Canal Olímpic s/n, 08860
> Castelldefels, Spain
> Room 1.02
> Tel : +34 93 645 29 12
> Fax : +34 93 645 29 01
> Email address: fermin dot galan at cttc dot es 
> 
> 
> 
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-- 
Stephen Hemminger <shemminger@xxxxxxxxxxxxxxxxxxxx>

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