[Intel-gfx] [PATCH] drm/i915: Park the GPU on module load

[Chris Wilson]

Quoting Chris Wilson (2018-09-14 10:47:36)
> Quoting Tvrtko Ursulin (2018-09-14 10:40:43)
> > 
> > On 14/09/2018 09:34, Chris Wilson wrote:
> > > Once we have flushed the first request through the system to both load a
> > > context and record the default state; tell the GPU to park and idle
> > > itself, putting itself immediately (hopefully at least) into a
> > > powersaving state, and allowing ourselves to start from known state
> > > after setting up all our bookkeeping.
> > 
> > Otherwise this would happen after a second or so, when the idle work 
> > handler does it. Crucial thing to mention is I think the park/unpark 
> > cycle which sets up the pinned default state.
> 
> Hmm, I didn't think it was worth highlight it here as one assumes that
> all the bookkeeping is equally required :) I pulled out for special
> mention in the comment, because I thought that was relevant to the
> function where we are acquiring the default_state.
>  
> > Alternative to patch could be to extract 
> > __intel_engine_pin_default_state to be called from here and from 
> > intel_engines_unpark.
> > 
> > But I guess there is some value in going powersave as soon as possible 
> > so okay.
> 
> Yeah. Later on (as in patches that have been on the ml for several
> months with feature requests depending on them...) we acquire a
> load_powersaving_context() function, which should make this a little more
> interesting.
> 
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> > > ---
> > >   drivers/gpu/drm/i915/i915_gem.c | 8 ++++++++
> > >   1 file changed, 8 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> > > index 89834ce19acd..be9d012d851b 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem.c
> > > @@ -5414,6 +5414,14 @@ static int __intel_engines_record_defaults(struct drm_i915_private *i915)
> > >   
> > >       assert_kernel_context_is_current(i915);
> > >   
> > > +     /*
> > > +      * Immediately park the GPU so that we enable powersaving and
> > > +      * treat it as idle. The next time we issue a request, we will
> > > +      * unpark and start using the engine->pinned_default_state, otherwise
> > > +      * it is in limbo and an early reset may fail.
> > > +      */
> > > +     __i915_gem_park(i915);
> > 
> > Why not after we have grabbed the default state?
> 
> I was just wanting to tie it to the switch to kernel-context + idle.
> I was thinking this was the closed point to the normal park sequence.
>  
> > I was worried this might access a sleeping device but apparently at 
> > least vma unbind takes the rpm ref. Still, just this I think makes it 
> > more logical to park after we have grabbed the default state, instead o 
> > putting the device to sleep and then immediately waking up below.
> 
> Oh, we have wakerefs aplenty on module load, we are not assuming gt.awake
> here.

I was very much mistaken!
-Chris