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

[Kamble, Sagar A]

On 12/30/2015 4:20 PM, Chris Wilson wrote:
> On Wed, Dec 30, 2015 at 04:09:46PM +0530, Kamble, Sagar A wrote:
>>     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.
> Remember that we quite frequently prevent the hardware going into RC6,
I assume this is threshold times in TO/EI mode for which GT is idle but 
not power gated.
> and that it has been known for the hardware to fail to enter RC6 itself
> (through driver error or whatnot).
And assume this is because of forcewake/rc6 setup errors in driver paths 
which should not happen in best case :)
Agree that running at Rpn makes sense.
>   Going to the extreme, why wouldn't
> you set Rp0 on idle, since that will give the best restart latency?
True. We can have different logic that starts from Rp0 and comes down if 
perf is met.
> -Chris
>
Thanks for the inputs Chris.