On Mon, Aug 25, 2014 at 3:22 AM, Jani Nikula wrote: > > [just moving from lkml to intel-gfx for a better fitting audience] > > On Mon, 25 Aug 2014, Jani Nikula wrote: > > On Fri, 22 Aug 2014, Eric Rannaud 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 > >> 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 V. Kelley Open Source Technology Center / SSG Intel Corp.