[Intel-gfx] [PATCH] drm/i915: Aggressively downclock Baytrail

[Chris Wilson]

On Thu, Jul 03, 2014 at 08:49:22AM -0700, Jesse Barnes wrote:
> On Thu,  3 Jul 2014 15:29:26 +0100
> Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 
> > Baytrail uses the RPS wait-boosting mechanism of Sandybridge+ but also has
> > a very lax downclocking strategy (upclock if more than 90% busy over 76ms,
> > downclock if less than 70% busy over 450ms). This causes Baytrail to use
> > maximum clocks, and for them to stay high, when doing simple tasks such as
> > scrolling through webpages. However, we can take a leaf out of the same
> > wait-boost mechansim and apply the aggressive downclocking strategy from
> > Sandybridge+ as well.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > ---
> 
> We really need a thorough test suite to cover stuff like this, mapping
> frequency, power, and total energy over a big set of workloads to make
> sure we're not adding big regressions.
> 
> I know you have the cairo traces, but did you also try this with a GL
> benchmark suite?

glxgears went from max clocks to min clocks whilst hitting 60fps.

Note that you first have to disable the cmdparser to make the machine
pleasant to use.

> I'm like the change (well you did mix in a cleanup to
> set_rps_thresholds),

Actually, I left it replicated originally because they used different
strategies at one point and keeping it separate eased experimentation.

The only thing that is missing is a comment to explain that I found I
needed to rewrite the control register every time for the change in
thresholds to take effect.

> I just want us to get better at collecting numbers
> for this stuff...

It's not like we have pretty tools to overlay realtime GPU usage and
bottlenecks...
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre