Re: [Xen-users] xen overhead - performance

[Ralph Passgang <ralph@xxxxxxxxxxxxx>]

Am Montag, 6. August 2007 11:21:13 schrieb Marco Strullato:
> Hi all!
> I have a question: what is the overhead of xen?

depends on what you are planning to do. If you use paravirtualisation (for 
linux guests), then the overhead is quite low. Maybe 1-5% (max).

If you use hvm (hardware virtualisation), then there is definitly a bigger 
performance loss.

> I mean, I'm going to install xen on servers with VT compatibile cpus
> (xeon) , raid5 disks and much ram. I will use logical volume to manage
> storage.
>
> what is the loss of cpu / disks /memory due to xen?
>
> For example now, without xen, servers are not much used but some days
> of the month I have to execute perfomance tests ( resourses used
> almost at 100%)
> After installing xen, I will have to do the same: I will stop every
> domains except for Dom0 and Dom1. So what loss of performance should I
> expect?

there is just on dom0 and many domUs... Something like a dom1 doesn't exist, 
at least xen doesn't name it like this.

If you just have dom0 and one domU running and dom0 doesn't need a lot of cpu, 
then domU should be just a little bit slower than on bare-metall (if you use 
paravirtualisation).

In general I would think that the benefit of using xen is bigger then the 
potential performance loss.

> Thanks
>
> Marco Strullato
>
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