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

Chris Wilson
2015-03-11T14:06:54Z

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?

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

--
Chris Wilson, Intel Open Source Technology Centre