[Intel-gfx] Why idle_freq is set to RPn and not RPe

Kamble, Sagar A sagar.a.kamble at intel.com
Wed Dec 30 02:39:46 PST 2015

Turbo frequency range is Rpe to Rp0 when GPU is active as, on workload 
submission frequency is taken to Rpe.

Does the HW require us to drop to RPn before entering RC6?
If we can enter RC6 even with other frequencies I think we can keep 
running at Rpe on Idle.

Only benefit of running at Rpn might be some additional power saving 
when workload is very lightweight. Is that correct Chris?


On 12/30/2015 3:20 PM, Szwichtenberg, Radoslaw wrote:
> Hello Chris!
> The question is: why this change in behavior was made?
> On previous platforms Gfx Turbo frequency selection range in driver was in between Rpe & Rp0. Since Rpe is the possible Fmax at Vmin, it was used as the starting frequency once driver booted and any value lower than that was not requested.
> Thanks!
> Radek
>> -----Original Message-----
>> From: Chris Wilson [mailto:chris at chris-wilson.co.uk]
>> Sent: Wednesday, December 30, 2015 10:31 AM
>> To: Kamble, Sagar A
>> Cc: S, Deepak; Szwichtenberg, Radoslaw; Intel Graphics Development; Goel,
>> Akash
>> Subject: Re: Why idle_freq is set to RPn and not RPe
>> On Wed, Dec 30, 2015 at 02:51:27PM +0530, Kamble, Sagar A wrote:
>>> Hi Chris,
>>> With below commit, idle frequency is made RPn (HW Min).
>>> Why are we not keeping it at RPe (Efficient Frequency)?
>>> My understanding was to set Rpe on idle so that when GPU is out of
>>> RC6 it can start operating at efficient frequency.
>> The driver is *idle*. When there is work to be submitted to the GPU, then
>> we go back to RPe (though we wait for it to wake up first). RPe is just an
>> inflexion point on the power curve.
>> -Chris
>> --
>> Chris Wilson, Intel Open Source Technology Centre

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