Re: [PATCH] drm/i915: Aggressively downclock Baytrail

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Thu, 3 Jul 2014 16:59:17 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> 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@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@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...

Yeah I know we have nice tools, I'm just thinking of data over time so
we can see regressions easily etc.  The power stuff QA collects ought
to catch it, but I don't think we've done specific runs with turbo
changes recently; would be good to get Wendy to do that for this patch
and see what happens.

-- 
Jesse Barnes, Intel Open Source Technology Center