Hi, On Tuesday 26 August 2014 16:00:51, Eric Rannaud wrote： > On Tue, Aug 26, 2014 at 1:59 PM, Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > >> Forcing FBC with i915.enable_fbc=1 brings the idle power consumption > >> back to under 7W, however. > >> This is all on 3.15.4-ARCH-00041-gf4db98240ac2. > > > > Any significant changes in package C state as reported in powertop? > > Indeed fairly impressive how much fbc saves here ... > > Not that I can tell. > Powertop report with FBC: http://pastebin.com/5qfJKpTQ > Without FBC: http://pastebin.com/NaYkR4n0 > > Some highly uneducated guesses on what could explain a +4W jump with no FBC: > > #1- The higher DRAM and bus duty cycle during scanout is enough to > prevent some DRAM subsystems from sleeping, by crossing some tight > threshold (maybe Apple has FBC enabled, so parameters somewhere in > firmware are tuned for the lower level of background activity they > expect with FBC on?). Not much we can do about that, unless such > parameters can be tweaked by us. > > #2- Without FBC, the FB doesn't fit in L3 (i7-4750HQ has 6MB, > 2880x1800 compressed at least 1:4 fits), keeping the DRAM awake more. > > #3- Disabling FBC somehow affects the layout of the framebuffer in > DRAM, keeping more of the DRAM active and awake during scanout. > Different tiling, swizzling, etc. parameters? Is it worth looking at > the code for that kind of thing? To be clear, I'm (blindly) suggesting > that it might be possible to increase the locality of the framebuffer > in physical DRAM, even without compression enabled. I notices similar behavior. From the output of turborstat, with FBC MBP can reach PC6 more than 90% of the time when idling, after FBC was disable in 3.14 or 3.15 the chip stays in PC2 and the estimated GPU power consumption is a few watts higher. -- Best Regards, LR _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
