Dual CPUs?

[krondor]

I read on your technology page that the VMs are supposed to be run on Dual AMD Opterons.

However, TOP will not display a second CPU and the kernel does not report SMP. Why am I unable to determine how many CPUs are in the VM environment? Does XEN virtualize the 2 CPUs as 1? Are you limiting Virtual Machines on a per CPU basis? Thanks for any information.

[krondor]

I misunderstood how XEN virtualizes the hardware. I had thought a big advantage of XEN versus UML and VMWare was the native hardware access, but I now understand that each XEN virtual machine still runs as a process on the host OS.

Which effectively means a XEN installation on a dual processor server with only one XEN virtual machine will only use 1 processor for that virtual machine. With 2 virtual machines each XEN process would get 1 processor. With 3 virtual machines the process requesting cpu resources gets the least loaded processor.. etc.. so basically like VMWare in that respect. Am I wrong?

[matta]

Sort of right, but not really. Xen itself is a hypervisor which boots and then it boots an administrative VM. Each extra VM then talks directly to the hypervisor... the admin VM is used for filesystems (LVM) and networking.

This allows multiple OS's to be run under a single system, but the OS's must bed ported to the "xen" arch. Due to this everything is very fast, multiple times faster than UML or VMware.

Right now each VM can only use a single CPU at a time, but since these are low power VM's that is not a problem... having access to both CPU's really isn't going to make much faster. In Xen 3.0 SMP will be supported in guest VM's.

[krondor]

Thank you for the response, very interesting stuff.

I think perhaps I would like to play with XEN on my own to get a better idea of how it differs from UML and VMWare (both of which I have configured before). It definitely (on paper at least) looks to be significantly superior. Companies like IBM and Novell don't just throw their weight behind any random old project, so it should have quite a good deal of potential.