Re: Why idle_freq is set to RPn and not RPe

From: "Kamble, Sagar A" <sagar.a.kamble@intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>,
	"Szwichtenberg, Radoslaw" <radoslaw.szwichtenberg@intel.com>,
	"S, Deepak" <deepak.s@intel.com>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	"Goel, Akash" <akash.goel@intel.com>
Subject: Re: Why idle_freq is set to RPn and not RPe
Date: Thu, 31 Dec 2015 23:08:17 +0530	[thread overview]
Message-ID: <56856809.4080604@intel.com> (raw)
In-Reply-To: <20151230105016.GW31221@nuc-i3427.alporthouse.com>


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.
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