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

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-09-14 11:03:03)
> 
> On 14/09/2018 10:47, Chris Wilson wrote:
> > 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.
> 
> Now I am having doubts if it is a business of 
> __intel_engines_record_defaults to park the engines, or the caller 
> (i915_gem_init) would be a better design..

Hmm, nah, you're just reading too much specificity into record_defaults
:-p
-Chris