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

Alain Williams addw at phcomp.co.uk
Sun Dec 9 17:41:00 UTC 2012

On Sun, Dec 09, 2012 at 05:27:34PM +0000, 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?

Buffer cache on the host machine ?

Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
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