RE: [Xen-users] low network performance

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

Sorry about the previous message - hit send before I should have.  

> 
> Thanks for the reply.
> But changing the txqueuelen on all doms to 512 dind't bring
> up some performance enhancements on my system.
> Well the value before was a 0 at domO  and 1000 at
>  domUs... what ever that
> means.
> 
> And i'm using the standard bridge-mode to connect the
> doms. But to get sure u may have a look at:
> http://www.neobiker.de/wiki/index.php?title=XEN_Netzwerk_f%C3%
> BCr_Firewall
> because i'm using this script for configuring the
> network.
> But as i understand this script uses bridging ...
> 
> Well, do u also have a one-core CPU, so the problem
> might be comparible to my or do u use a
> dualcore-/quadcore-cpu or dual/quad-system with single
> CPUs ? 
> This point is interesting for me anyway, because in a
> previous mail a Xen-USer told me about that the
> performance would be much better on such a system.

That was me, and the reason I believe this will help is simply that
there are three "processes" running when you do DomU-DomU network
traffic, and none of the traffic actually hit a real network device ever
- it's all about software that copies data from one place to another
(and the relevant cross-domain interactions to wake the next domain,
etc). 

> 
> So therefore i want to ask all of U@list what kind of
> system are u using and how good the performance is? 
> So do u use ...
> a) a antiquated ;) single-core single CPU system as i
> do ? 
> b)
>  'normal' dual singlecore-cpu System ?
> c) 1 dualcore/quadcore cpu ?
> d) more then 1 dualcore/quadcore cpu ? ... maybe 4 of
> them :O ? ... don't wanna know how big the overhead
> might be in this case :X 

For optimal system performance, you want at least Dom0 to have it's own
CPU-core (or at the very very least it's own hyperthread, so at least
the registers don't need reloading). 

Having at least two cores will help quite a bit - and that's what I'm
using for my development work. [But I don't sit and measure network
performance daily - or at all, really. As long as I can connect my
machine to the corporate network, I'm happy - and for many purposes, the
corporate network is more of an issue than the data-transfer between my
local machines anyways]. 
> 
> And basically which version would u suggest to run the
> best performance? furthermoire i'd like to know if there is a 
> important performance difference between a AMD or Intel system ?

There isn't a BIG difference for otherwise comparable CPU's (e.g
comparing dual core of similar[1] speeds gives similar results,
comparing a dual core to a quad core isn't really fair!

One thing to consider is that running Xen (or any other virtualization
platform) will use more memory, and memory bandwidth becomes a more
important factor than in this case than under a single OS. 

[1] Note that we shouldn't really use MHz as a "speed" comaparator, as
that is only useful within a particular processor model - different
models have different "performance per MHz". Unfortunately, there is no
unbiased other measurement - so the only real solution is to look at
(independent) benchmarks that are doing the same or similar task(s) as
you want to do on your machine. 

> 
> Allthough i'm not in the situation (as a poor student)
> to spend some hundred bucks for a new system :( i'm
> interested in that point ... U'll never know where u
> find some money ;) 

I would personally recommend a low-end AM2 Dual Core processor and
related motherboard/memory. [Somehting like a 3800+ AM2 processor isn't
very expensive]. A quick google found someone selling a Motherboard +
processor + 2GB DDR2 memory for just under $300 - this may not be the
best price available, but it's a guide to the pricing of this [and you
being in Germany will of course have to find a better place than the US
to buy it, as US prices may be all well and good, but shipping will most
likely kill any benefit of lower US prices... ]

The AM2 processors (except for Sempron models) also let you use the HVM
(full virtualization) mode that will allow you to run Windows, OS/2 or
any other OS that hasn't been "Xenified" yet. 

--
Mats



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