Ben, unfortunately this is the default Ubuntu kernel without this feature.
You need to use version 3.16.0-28.37hf73386v20141212b2 to be able to benefit from it.
Do install this version you should do: sudo apt-get install linux-image-3.16.0-28-generic=3.16.0-28.37hf73386v20141212b2
and then choose this kernel from the GRUB boot menu.
Ben, unfortunately this is the default Ubuntu kernel without this feature.
You need to use version 3.16.0- 28.37hf73386v20 141212b2 to be able to benefit from it.
Do install this version you should do: 3.16.0- 28-generic= 3.16.0- 28.37hf73386v20 141212b2
sudo apt-get install linux-image-
and then choose this kernel from the GRUB boot menu.