Re: Fwd: [Bug 92111] Power regression from 3.17 to 3.18 and 3.19

[Matthew Garrett <mjg59@srcf.ucam.org>]

On Wed, Feb 11, 2015 at 02:02:06AM +0100, Rafael J. Wysocki wrote:
> On Wednesday, February 11, 2015 12:33:18 AM Matthew Garrett wrote:
> > We're using intel_idle, so we should be making idle state determination 
> > regardless of what ACPI tells us. So is Darwin mode influencing the 
> > state of some MSR that controls whether PC6 can be entered?
> 
> I need to confirm that with Len, but I don't recall there being an MSR
> controlling the PC6 availability on Haswell.  There is one for PC7, but
> not for PC6 IIRC.

Ok.

> > Is the GPU blocking it because of some configuration difference?
> 
> That is possible.

I know that it has some say in things here.

> > I don't know enough about how the chip decides to enter PC6 to be able to
> > tell.
> 
> Well, so honestly how do you expect me to respond here?

We really need feedback from people who know how the CPU makes its PC6 
determination - the firmware has clearly done something differently, but 
without knowing what factors feed into that determination we're pretty 
much helpless.

-- 
Matthew Garrett | mjg59@srcf.ucam.org