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

Deepak S
2015-05-08T15:09:34Z

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@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

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