Re: [PATCH 3/5] drm/i915/chv: Set min freq to efficient frequency on chv

From: Deepak S <deepak.s@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH 3/5] drm/i915/chv: Set min freq to efficient frequency on chv
Date: Wed, 11 Mar 2015 19:59:56 +0530	[thread overview]
Message-ID: <55005164.4020700@linux.intel.com> (raw)
In-Reply-To: <20150311140650.GC13727@nuc-i3427.alporthouse.com>

On Wednesday 11 March 2015 07:36 PM, Chris Wilson wrote:
> On Wed, Mar 11, 2015 at 07:23:48PM +0530, Deepak S wrote:
>>
>> On Thursday 26 February 2015 09:42 PM, Chris Wilson wrote:
>>> On Thu, Feb 26, 2015 at 08:46:56PM +0530, deepak.s@linux.intel.com wrote:
>>>> From: Deepak S <deepak.s@linux.intel.com>
>>>>
>>>> After feedback from the hardware team, now we set the GPU min freq to RPe.
>>>> If we drop the freq to RPn, we found that the punit was not setting the
>>>> voltage to Vnn, So recommendation is to set min freq to RPe.
>>> And does it change the voltage at all?
>> Yes Voltage does change when we drop to RPe
>>
>>> Is there really any advantage to
>>> the extra code on idle?Does efficient_freq really consume less power
>>> than min_freq when active (assuming a min_freq/efficient_freq busy
>>> workload i.e. does a workload that would be 100% busy at min_freq
>>> consume less power when run at efficient_freq)?
>> The delta voltage usage between RPn and RPe is very small like close to zero.
>> Also, if we run workload 100% busy at Rpe we get better performance without much of voltage loss right?
>> btw, Punit expects us to operate between Rpe & RP0.
> If you need 100% at RPe you obviously can't run at RPn (since that would
> lead to dropped frames). The question is if you have a workload that
> requires 100% at RPn do you save power if you ran e.g. 80% at RPe?

We do not expect much of power saving running at RPn.
If we need exact number I need to gather the data.

>
> If the punit only works reliably between RPe and RP0, then the current
> RPn is a bit of a misnomer, and that should be the explanation in the
> commit log. Definitely do not conflate the idea of executing at RPn and
> RPe with the idea of idling at RPn or RPe - this patch affects idle
> frequency.
> -Chris
>
Yes I understand it affects idle freq but running at RPe gives better performance at lower voltage and also punit drops voltage to help save power
I will update the commit msg to explain why we need lower freq at Rpe.

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