[Intel-gfx] [PATCH 1/2] drm/i915: Re-add enable_rc6 modparam

[Ville Syrjälä]

On Fri, May 17, 2019 at 09:44:46AM -0700, Rodrigo Vivi wrote:
> On Fri, May 17, 2019 at 07:34:23PM +0300, Ville Syrjälä wrote:
> > On Fri, May 17, 2019 at 09:17:39AM -0700, Rodrigo Vivi wrote:
> > > On Thu, May 16, 2019 at 03:49:19PM +0000, Summers, Stuart wrote:
> > > > On Thu, 2019-05-16 at 18:42 +0300, Jani Nikula wrote:
> > > > > On Thu, 16 May 2019, "Summers, Stuart" <stuart.summers at intel.com>
> > > > > wrote:
> > > > > > On Thu, 2019-05-16 at 12:59 +0300, Jani Nikula wrote:
> > > > > > > On Tue, 14 May 2019, Rodrigo Vivi <rodrigo.vivi at intel.com> wrote:
> > > > > > > > One possibility that just came to my mind now is, what if we
> > > > > > > > make
> > > > > > > > this only for platforms that are still protected by
> > > > > > > > is_alpha_support=1
> > > > > > > > (soon becoming require_force_probe=1)
> > > > > > > 
> > > > > > > Please don't conflate alpha_support or force_probe with
> > > > > > > *anything*
> > > > > > > else.
> > > > > > > 
> > > > > > > > But this is just one side of the coin... when product is out
> > > > > > > > there
> > > > > > > > and we want the user to debug the issue to see if it is a RC6
> > > > > > > > bug
> > > > > > > > we have no way to verify that. :/
> > > > > > > 
> > > > > > > The problem is, if it works with rc6 disabled, it doesn't prove
> > > > > > > it's
> > > > > > > an
> > > > > > > rc6 bug either.
> > > 
> > > Well, RC6 is the main GT power gating. The issue could be on may other
> > > individual power gating, but if by disabling RC6 the issue is gone
> > > it is a very good indication that it is a GT-PM bug somewhere.
> > 
> > I disagree. In the recent past enable_rc6 was often used by
> > people to workaround display underruns and whatnot.
> 
> o.O
> do you mean this was being used as a placebo? or real issue?
> or something like by keeping rc6 gpu was keeping the power request
> to punit high so display was receiving enough power to not strugle
> with wm? or something like that or what?

Disabling rc6 disables most package C-states, which makes life
a lot easier for the display engine due to reduced memory
access latencies.

-- 
Ville Syrjälä
Intel