i915 update to Linux 3.8 ready!

[Ed Maste]

On 9 March 2016 at 20:06, Ed Maste <emaste at freebsd.org> wrote:
> On 8 March 2016 at 16:07, Jean-Sébastien Pédron <dumbbell at freebsd.org> wrote:
>> Hi!
>>
>> The i915 update is now in HEAD as of r296548:
>> https://lists.freebsd.org/pipermail/svn-src-head/2016-March/083332.html
>
> Thank you very much Jean-Sébastien for bringing this to completion!
>
> I've now updated my regular laptops to HEAD after this commit and have
> discovered that the power consumption seems to have increased
> significantly.

I found reports that Linux introduced a regression on Sandy Bridge
power consumption sometime around Linux 3.6 that was fixed after 3.8.
Those reports are specifically for an increase after a suspend-resume
cycle; something gets confused and causes the GPU to never enter rc6.
It's not exactly the same symptom, as I see increased consumption
after reboot and loading i915 (before starting X), but certainly seems
related.

Anyhow, with that patch applied after a suspend-resume cycle I'm back
to a reasonable power consumption -- around 15W in X with Firefox
running. The patch is in https://reviews.freebsd.org/D5599.