Linux Ethernet Bridging - May 2007 - [Bridge] Performance and limitations of virtual bridges

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?

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).

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.
 
Thanks in advance!

Best regards,

--------------------
Ferm?n Gal?n M?rquez
CTTC - Centre Tecnol?gic de Telecomunicacions de Catalunya
Parc Mediterrani de la Tecnologia, Av. del Canal Ol?mpic 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

On Mon, 7 May 2007 20:32:17 +0200
Ferm?n Gal?n M?rquez <fermin.galan@cttc.es> 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,
> 
> --------------------
> Ferm?n Gal?n M?rquez
> CTTC - Centre Tecnol?gic de Telecomunicacions de Catalunya
> Parc Mediterrani de la Tecnologia, Av. del Canal Ol?mpic 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@linux-foundation.org>