pcbsd9-stable-20120505 snapshot - howto enable intel rc6

[user10508 at gmail.com]

I'm using this pcbsd snapshot on an asus k53e laptop

/etc/make.conf contains:
WITH_NEW_XORG=yes

xf86-video-intel-2.17.0 compiled from ports

Laptop runs very hot
Battery lasts less than half as long as pcbcd9 release intel driver

sysctl inquiry reveals

hw.dri.0.info.i915_drpc_info: RC information accurate: yes
Video Turbo Mode: yes
HW control enabled: yes
SW control enabled: no
RC1e Enabled: no
RC6 Enabled: no
Deep RC6 Enabled: no
Deepest RC6 Enabled: no
Current RC state: on
Core Power Down: no


If it is possible to enable RC6:

what modes can be enabled

how can/should an RC6 mode be enabled

TIA