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Re: [Xen-users] virtualbox vs. xen - ease of domU installation

  • To: "Freddie Cash" <fjwcash@xxxxxxxxx>
  • From: "Grant McWilliams" <grantmasterflash@xxxxxxxxx>
  • Date: Thu, 15 May 2008 13:45:13 -0700
  • Cc: xen-users@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Thu, 15 May 2008 13:45:50 -0700
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On Thu, May 15, 2008 at 1:09 PM, Freddie Cash <fjwcash@xxxxxxxxx> wrote:
On May 15, 2008 11:54 am Miles Fidelman wrote:
> I've just started playing with Virtualbox - and boy do they make
> installing virtual machines easy.  Download an .iso of a netinstall CD,
> point Virtualbox at it, and you have a window that behaves just like a
> normal install.  Worked like a charm with both Debian Sarge and Etch
> images - doesn't seem to require any special bits in the guest O/Ss.

VirtualBox is based on a modified QEmu.  It emulates a complete computer,
right down to the BIOS, including a bunch of standard hardware
components.  As such, you don't need to modify OSes to run then on the VB
VM.  VirtualBox doesn't (AFAIK) use the hardware virtualisation support
in Intel/AMD CPUs, and does a bunch of software tricks to run the VMs.
Not sure if it uses the KQemu accelerator module or not, or anything
similar.  As such, running VMs in VirtualBox will be slower than other
solutions (that uses accelerator modules, hardware virtualisation
support, etc).

Freddie Cash

From VirtualBoxes website.  Seems they're using VT some but only when it's faster than their own optimizations (kqemu?).
"Since, however, nearly all operating systems in use today only make use of ring-0 and ring-3, and since a lot of operations in non-root mode are very expensive, VirtualBox does not use VT-x exactly as intended by Intel. Instead, we make partial use of it -- only where it makes sense and where it helps us to improve performance."

I've seen benchmarks (lies and damn lies) that show kqemu keeping up with KVM in some circumstances so this makes me wonder too. Is it just smoke and they haven't implemented full virtualization or are they really able to do some things faster using software tricks?

I'm getting ready to post to all VM mailing lists for recommended tests and optimizations. I'd like to do a full battery of tests against VMWare (if I'm allowed by law!), Xen, KVM, Kqemu, Parallels and VirtualBox to see where they fall in terms of performance. Of course I'll test multiple configurations like PV drivers, PCI passthrough etc.. so each will run as fast as it can.

It will be a huge undertaking but I'm curious as I think everyone else is. Most benchmarks aren't objective at all. Maybe I'll end up with a dead horse in my bed for doing this. :-)


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