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

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On Wednesday 06 May 2015 02:32 PM, Daniel Vetter wrote:
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@xxxxxxxxxxxxxxx wrote:
From: Deepak S <deepak.s@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx>
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

Hi Daniel,

Dynamic power bias is not supported by the HW or FW :(.
This static bias was recommended by HW team after analyzing the results on IA & GT

Thanks
Deepak

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