[GLLUG] How can a VM be faster than raw hardware?

Phil Dobbin bukowskiscat at gmail.com
Sun Dec 9 18:32:18 UTC 2012

On 12/09/2012 05:27 PM, John Winters wrote:

> I've just noticed something odd which puzzles me.
> For a while I've been developing a Rails application, using rspec to run
> the automated tests.  It's at an early stage, but to run the 212
> examples on my development machine currently takes about 38 seconds.
> The machine has a Core i5 3570K (3.4GHz), 16G of RAM and an SSD
> providing the development area.
> Because I need to play with it elsewhere, I just git cloned the source
> onto a Linux virtual machine running under VirtualBox on top of MacOS on
> a laptop.  The laptop is a much lower spec - 2.4 GHz Core 2 Duo, with
> only 1G of RAM available to the VM (4G in the machine in total), and a
> conventional spinning HDD.
> I was concerned about how long the test suite would take on the laptop,
> but to my surprise it runs in only 29 seconds.
> Anyone any idea why the lower spec machine would be so much faster?

Wow, that does surprise me. Virtualbox on my Macbook Pro 2.4 GHz Core 2
Duo is as slow as a dog.

It'd be interesting to see what speed the test runs on a kvm or xen vm.



currently (ab)using
CentOS 5.8 & 6.3, Debian Squeeze & Wheezy, Fedora Beefy & Spherical,
Lubuntu 12.10, OS X Snow Leopard & Ubuntu Precise & Quantal

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