RE: [Xen-users] Maximum number of interfaces in DomU

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: Igor Chubin [mailto:igor@xxxxxxx] 
> Sent: 27 March 2007 13:31
> To: Petersson, Mats
> Cc: Igor Chubin; xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: Re: [Xen-users] Maximum number of interfaces in DomU
> 
> On Di, Mär 27, 2007 at 02:24:20 +0200, Petersson, Mats wrote:
> 
> ...
> > > Does anybody know something about 
> > > the restriction of 3 network interfaces
> > > in domU that was discussed here:
> > > 
> > > http://lists.xensource.com/archives/html/xen-users/2006-05/msg
> > > 00024.html
> > > http://lists.xensource.com/archives/html/xen-users/2006-08/msg
> > > 00968.html
> > > 
> > > 
> > > Please tell, is the problem solved?
> > 
> > No, and there is no plan to "solve" this "problem". 
> 
> 
> Quotes around the words solve and problem
> mean that this is not a problem at all?

Well, that obviously depends on how you look at it. It is of course considered 
a problem by some people. But it's not considered a problem by the Xen 
developers community, I think, because no one has so far come up with a good 
argument why you actually need a GUEST to have more than three virtual 
interfaces. It's not limiting the bandwidth (which three physical connectors 
could perhaps do), because the speed of each interface is limited only by CPU 
and memory access speed in the guest and Dom0. It is of course limiting the 
number of different sources that guest can get data from with only the 
interface as a the distinguishing factor. 

Can you explain what the setup is where you need this, and why you need more 
than three virtual devices? It may help forward the argument for a fix, but 
there may also be others who have the solved the same sort of problem within 
the community here, without using more than three interfaces.

[Just to note: The reason it's limited to 3 interfaces is simply that's how 
many fit into one 4KB memory section, which makes it easy to manage in the 
code. Adding more interfaces would be possible, but it would complicate matters 
by some amount, as the interface between Dom0 and DomU is based on physical 
memory pages, and sending a list of those will make not only break backwards 
compatibility, but also complicate the common case of using (up to) three 
interfaces]. 

Finally, I'm indeed a Xen developer, but I've got very little to do with 
virtual network interfaces, so I may not have grasped the whole reasoning why 
this limit is and if/how difficult it is to change, nor any other complications 
or other issues involved. I also have not been involved in the decision to "not 
solve this problem". 

But I believe that if this was actually a REAL PROBLEM to a lot of people, then 
it would have been solved a long time ago. It may be a case of "yes, it's 
possible to solve, but not enough people are asking for it", or it may simply 
be that it's "not a real problem". 

--
Mats
> 
> -- 
> WBR, i.m.chubin
> 
> 
> 
> 



_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users