[Intel-gfx] i915: Regression: +4W in idle power use on Macbook Pro 15 (late 2013)

[Jani Nikula]

[just moving from lkml to intel-gfx for a better fitting audience]

On Mon, 25 Aug 2014, Jani Nikula <jani.nikula at intel.com> wrote:
> On Fri, 22 Aug 2014, Eric Rannaud <eric.rannaud at gmail.com> wrote:
>> Hi,
>>
>> Between 3.15.4 and 3.15.8, there was an increase in idle power consumption on
>> Apple Macbook Pro 15 (late 2013) on a freshly booted system (no wifi driver
>> loaded; brightness set to 4/100; X running; no desktop environment, except
>> Awesome), from 6.5W to about 10.5W, as reported by powertop.
>>
>> In the stable tree, it bisects to:
>>         commit f4db98240ac2c6d9d2118c6f82d483ff5293f1ed
>>         Author: Chris Wilson <chris at chris-wilson.co.uk>
>>         Date:   Fri Jun 6 10:37:11 2014 +0100
>>
>>             drm/i915: Disable FBC by default also on Haswell and later
>>
>>             commit 0368920e51ae0cded0eb518c340a4dd17764d461 upstream.
>>
>>             It causes black screen on bootup and is approximately 100x
>> slower than
>>             running with FBC disabled, so the GPU runs at a high
>> frequency for much
>>             longer - completely contrary to the power saving claims.
>> It also still
>>             has mutex deadlocks in multi-head scenarios, which can lead to a
>>             system/X lockup. These bugs were known before FBC was
>> enabled by default
>>             on Haswell and still have not been fixed.
>>
>> The issue is still present in Linus' tree (v3.17-rc1-22-g480cadc2b7e0).
>>
>> With a 75Wh battery, that's a significant loss in battery life in normal use.
>>
>> I'll be happy to help test any potential fix.
>
> The earlier regression trumps, and in this case it was enabling FBC by
> default on Haswell. Sorry.
>
> You can enable FBC with i915.enable_fbc=1 module parameter, but all bets
> are off. See the commit message you quoted above. I don't recommend.
>
> BR,
> Jani.
>
>
> -- 
> Jani Nikula, Intel Open Source Technology Center

-- 
Jani Nikula, Intel Open Source Technology Center