On Mon, Aug 25, 2014 at 3:22 AM, Jani Nikula <jani.nikula@xxxxxxxxx> wrote:
[just moving from lkml to intel-gfx for a better fitting audience]
On Mon, 25 Aug 2014, Jani Nikula <jani.nikula@xxxxxxxxx> wrote:
> On Fri, 22 Aug 2014, Eric Rannaud <eric.rannaud@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
>> 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.
>
For what it's worth, I have a Mid-2014, Macbook Pro Retina (13inch display), running Archlinux with 3.16.
Definitely, enable_fbc is a win for me and I do manually enable it. But I am still seeing what I believe to be
a regression overall of about +4W even with fbc enabled. Still digging for clues.
Sean
Sean
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