Re: [PATCH v3] drm/i915: Setup static bias for GPU

Daniel Vetter
2015-05-06T09:00:40Z

On Tue, May 05, 2015 at 01:12:41PM +0530, Deepak S wrote:
>
>
> On Monday 04 May 2015 08:58 PM, Ville Syrjälä wrote:
> >On Mon, May 04, 2015 at 10:12:23AM +0200, Daniel Vetter wrote:
> >>On Mon, May 04, 2015 at 10:58:02AM +0530, Deepak S wrote:
> >>>
> >>>On Wednesday 29 April 2015 02:59 PM, Ville Syrjälä wrote:
> >>>>On Wed, Apr 29, 2015 at 08:36:24AM +0530, deepak.s@linux.intel.com wrote:
> >>>>>From: Deepak S <deepak.s@linux.intel.com>
> >>>>>
> >>>>>Based on the spec, Setting up static BIAS for GPU to improve the
> >>>>>rps performace.
> >>>>>
> >>>>>v2: rename reg defn to match spec. (Ville)
> >>>>>
> >>>>>v3: Updated bias setting for chv (Deepak)
> >>>>>
> >>>>>Signed-off-by: Deepak S <deepak.s@linux.intel.com>
> >>>>Matches the spec. Whether the chosen bias is really the best, I can't
> >>>>really say. But favoring the GPU does seem like a sensible idea if we
> >>>>want to keep the UI stuff fluid enough while there's some CPU heavy
> >>>>tasks running at the same time.
> >>>>
> >>>>Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>>Thanks Ville for reviewing,
> >>>Yes our aim is to keep user experience smooth.
> >>Since the aim is smooth UI ... how does this interact with the rps
> >>boosting that was just enabled with Chris' patches for vlv/chv too?
> >>
> >>A static bias seems a lot less what we want now that we should have
> >>something dynamic. Specifically I'm thinking of
> >>
> >>commit 6ad790c0f5ac55fd13f322c23519f0d6f0721864
> >>Author: Chris Wilson <chris@chris-wilson.co.uk>
> >>Date: Tue Apr 7 16:20:31 2015 +0100
> >>
> >> drm/i915: Boost GPU frequency if we detect outstanding pageflips
> >Totally separate topic. This only affects how the Punit splits up the
> >available energy credits between the CPU and the GPU. So only relevant
> >when thermally constrained and both CPU and GPU would like to run
> >faster than the limit allows.
> >
> Thanks Ville.
>
> This is completely a different topic, more to do with punit budget
> constraints & this does not impact "Boot RPS logic"

Well I thought it'd be related since the justification was better UI
interactivity. And that tends to not be a thermal constrained load but
something really spike-y. And a static bias doesn't seem like a solution
to that problem.

I'll just go ahead and merge, but still feels like at least I don't know
why exactly we need this.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation