[ltp] Lower power consumption with upcoming 2.6.33

[Tino Keitel]

On Mon, Jan 25, 2010 at 09:17:26 +0100, Frédéric Boiteux wrote:

[...]

>   Thanks for your report. Do you have any clue about where power is
> saved ? do you think a specific peripheral is better handled ? or the
> kernel just do its tasks in a more efficient way ?

With older kernels, I noticed that the temperature sensor 4 seemed to
be connected to the fan going on or off if the laptop was idle. This
sensor seems to be located at the GPU, which is Intel i965 in my case.
There were some commits which are aimed to reduce the power consumption
of Intel GPUs, especially this:

commit 97f5ab6651a996ecefed73e41684422f3b29d9a8
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Thu Oct 8 10:16:48 2009 -0700

    drm/i915: add render standby support
    
    Render standy allows the GPU to power down the render unit
    whenidle.  In order for this to work, it needs a page of graphics
    memory to save state.  This patch allocates that page and enables
    the feature on supported chipsets.

It seems to be effective for i965 and newer chips:

+#define I915_HAS_RC6(dev) (IS_I965GM(dev) || IS_GM45(dev) || IS_IGDNG_M(dev))

With 2.6.33, the fan runs much less often, and sensor 4 is genererally
at lower values, which also indicates less power consumption in the
GPU.

Regards,
Tino