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:

quoted

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.

quoted

Is the GPU blocking it because of some configuration difference?

That is possible.

I know that it has some say in things here.

quoted

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