Re: [PATCH] drm/i915: use hsw rps tuning values everywhere on gen6+

[Daniel Vetter <daniel@ffwll.ch>]

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@bwidawsk.net>
> Cc: stable@vger.kernel.org
> Signed-off-by: Daniel Vetter <daniel.vetter@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@ffwll.ch
Mobile: +41 (0)79 365 57 48