Comment 3 for bug 1384867

Same problem here (Ubuntu 14.10, AMD64).
Here it seems to be related with Intel P-state:
http://www.webupd8.org/2014/04/10-things-to-do-after-installing-ubuntu.html (1.5 section)

Here a benchmark about using or disabling Intel P-state:
http://www.phoronix.com/scan.php?page=article&item=intel_pstate_linux315&num=1

To solve this bug:
gksu gedit /etc/default/grub
than change
GRUB_CMDLINE_LINUX_DEFAULT="quiet ... ..."
to
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash intel_pstate=enable"

Obvoiusly this will disable Intel P-state