[fedora-virt] slightly OT: Comparing apples with apples?

[Mark McLoughlin]

Hi Gianluca,

On Fri, 2009-04-24 at 09:15 +0200, Gianluca Sforna wrote:
> Hi all,
> sorry for the slightly off topic post, but I'm looking for some
> definitive answers here.
> A couple days ago, I performed a "boot race" with Fedora 11 and Ubuntu
> 9.04, thinking it would be the easiest way to visualize which is
> faster to boot in a default installation.
> So basically, I created two identical VMs with virt manager and
> installed both from the liveCD, then fully updated them.
> The recorded boot sequence was repeated multiple times to see if
> results were consistent.

That's crazy talk! How could you possibly hope to get any useful results
from such a stupid experiment. VMs aren't real machines, dude!

> Now, of course I hit a nerve there, because I had many complaints,
> ranging from the video being a fake, to personal attacks, to more or
> less weird attempts to explain why Fedora booted faster.

Fedora booted faster? Wait, I take it back, that's a wonderful
experiment! :-)

> The most common complain was that competing for the host's resources
> was not fair, something along the line: Fedora starts first becasue
> has no grub, grabs some critical resource and Ubuntu has to wait for
> it before continuing.
> 
> So basically the question is: do you think there could be any reason
> why such a test can be unfair to one of the VMs?

Okay, seriously - I think it's a reasonable experiment.

However, the fact that you have two guests competing for resources is
always going to make people suspicious. It may well be a deterministic
experiment, but you're always going to have a hard time convincing
people of that.

Personally, I'd do it by timing each VM on its own and comparing the
boot times.

Also, I personally wouldn't be interested in which is faster boot, but
rather what the bottlenecks are in both cases and how to make them both
boot faster.

Cheers,
Mark.