[Bug 100572] [SKL dmc] Headless mode media transcoding is 20-30% slower comparing to connected monitor use case

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=100572

--- Comment #26 from Imre Deak <imre.deak at intel.com> ---
(In reply to Tvrtko Ursulin from comment #25)
> One of the experiments Animesh asked me to do was to look at the state of
> the DC_STATE_EN register at runtime.
> 
> It looked that it had reverted to a value other than what was programmed by
> i915. On top of that, it looked impossible to manually modify it at runtime.
> 
> The value it is reverting to was DC_STATE_EN_UPTO_DC6, regardless of whether
> the driver has programmed DC_STATE_EN_UPTO_DC5 or DC_STATE_EN_UPTO_DC5 |
> DC_STATE_EN_UPTO_DC6.
> 
> This coupled with a comment in gen9_write_dc_state makes me suspicious
> whether DMC is not doing things behind the drivers back?

We don't use DC5 on SKL normally only DC6. Did you boot with i915.enable_dc set
to something non-default?

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