On Wed, Aug 15, 2012 at 10:41:45AM +0200, Daniel Vetter wrote: > James Bottomley reported [1] a massive power regression, due to the > enabling of semaphores by default in 3.5. A workaround for him is to > again disable semaphores. And indeed, his system has a very hard time > to entre rc6 with semaphores enabled. > > Ben Widawsky run around with a kill-a-watt a lot and noticed: > - There are indeed a few rare systems that seem to have a hard time > entering rc6 when desktop-idle. > - One machine, The Indestructible Toshiba regressed in this behaviour > between 3.5 and 3.6 in a merge commit! So rc6 behaviour with the > current setting seems to be highly timing dependent and not robust > at all. > - The behaviour James reported wrt semaphores seems to be a freak > timing thing that only happens on his specific machine, confirming > that enabling semaphores shouldn't reduce rc6 residency. > > Now furthermore the Google ChromeOS guys reported [2] a while ago that > at least on some machines a simply a blinking cursor can keep the gpu > turbo at the highest frequency. This is because the current rps limits > used on snb/ivb are highly asymmetric. > > On the theory that gpu turbo and rc6 tuning values are related, we've > tried whether the much saner looking (since much less asymmetric) rps > tuning values used for hsw would also help entering rc6 more robustly. > > And it seems to work. > > Reference[1]: http://lists.freedesktop.org/archives/dri-devel/2012-July/025675.html > Reference[2]: http://lists.freedesktop.org/archives/intel-gfx/2012-July/018692.html > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=53393 > Tested-by: Ben Widawsky <ben at bwidawsk.net> > Cc: stable at vger.kernel.org > Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch> Ok, I've merged this one here, making the commit message a bit more cautious. Unfortnately we don't seem to have the understanding (nor the resources to gain it) of the hw to do better than copy&paste what we get from the hw team :( -Daniel -- Daniel Vetter Mail: daniel at ffwll.ch Mobile: +41 (0)79 365 57 48
