[CentOS] CentOS 6 : Tip for significantly increasing battery life / reducing power consumption (Thinkpad X220 Tablet)

Sat Aug 4 03:23:25 UTC 2012
James A. Peltier <jpeltier at sfu.ca>

----- Original Message -----
| Hello,
| I was not happy with the power consumption of CentOS 6 x86_64 on a
| new
| Lenovo Thinkpad x220 Tablet and I worked on reducing it. I just
| wanted
| to share with the list one of the changes which gave me the most
| significant improvement.
| As per http://www.williambrownstreet.net/blog/?p=387, add the
| following kernel arguments to the GRUB boot configuration:
| pcie_aspm=force i915.i915_enable_rc6=1 i915.lvds_downclock=1
| i915.i915_enable_fbc=1
| (in /boot/efi/EFI/redhat/grub.conf since I use EFI,
| /boot/grub/grub.conf otherwise)
| As measured using PowerTop, this made the power consumption decrease
| from 20W to 11W !
| (I had already decreased it from 25W to 20W with the usual tips of
| disabling hardware, shutting down services, switching tuned profiles,
| etc.)
| All in all, battery time was more than multiplied by two, and the
| computer is now much more silent since the fan is not always running
| like mad in order to cool the processor. The bottom of the laptop is
| not anymore hot as hell.
| I don't know whether this would have an impact on other hardware, but
| it may be worth looking at it (even on servers?), since the above
| link
| points to descriptions of a regression in the kernel which seems more
| general.
| As a side note, the Power Management Guide of Red Hat is a good
| resource (analysis tools + tuned profiles):
| http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html-single/Power_Management_Guide/
| Cheers,
| Mathieu
| PS: Do you think I should book a bug in the upstream bug tracker?
| _______________________________________________
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You could also consider just sticking to tuned and then having a look at the power management options as provided there.  tuned-adm list will show you some predefined power management options which *can* be tweaked.

Do you know what those options due to your machine in order to make the battery last longer?  I mean really, do you know what they do?  

These could be bad options for a number of users and since it's set at kernel boot time how can you override it once the OS has booted?  Can you disable this without altering boot parameters and rebooting?  If the answer is yes than a tuned configuration should be created or altered to set them dynamically.  Setting of these at boot time are likely just wrong.  You likely only want these to be turned on when the laptop is not attached to power, which you can create hooks for.

This is not a bug, it's a feature/workaround on specific hardware, that tweaks specific settings to get around a specific issue with the driver.  Create a profile and submit it upstream.

James A. Peltier
Manager, IT Services - Research Computing Group
Simon Fraser University - Burnaby Campus
Phone   : 778-782-6573
Fax     : 778-782-3045
E-Mail  : jpeltier at sfu.ca
Website : http://www.sfu.ca/itservices

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