[Intel-gfx] [PATCH 02/11] drm/i915/gtt: Teach restore-gtt to walk the ggtt vma list not the object list

[Chris Wilson]

Quoting Joonas Lahtinen (2018-06-05 08:51:39)
> Quoting Chris Wilson (2018-06-05 10:19:40)
> > In preparation, for having non-vma objects stored inside the ggtt, to
> > handle restoration of the GGTT following resume, we need to walk over
> > the ggtt address space rebinding vma, as opposed to walking over bound
> > objects looking for ggtt entries.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> > Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> > Cc: Matthew Auld <matthew.william.auld at gmail.com>
> 
> Comment below.
> 
> Reviewed-by: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> 
> > @@ -3578,21 +3578,15 @@ void i915_gem_restore_gtt_mappings(struct drm_i915_private *dev_priv)
> >         ggtt->vm.closed = true; /* skip rewriting PTE on VMA unbind */
> >  
> >         /* clflush objects bound into the GGTT and rebind them. */
> > -       list_for_each_entry_safe(obj, on, &dev_priv->mm.bound_list, mm.link) {
> > -               bool ggtt_bound = false;
> > -               struct i915_vma *vma;
> > -
> > -               for_each_ggtt_vma(vma, obj) {
> > -                       if (!i915_vma_unbind(vma))
> > -                               continue;
> > +       GEM_BUG_ON(!list_empty(&ggtt->vm.active_list));
> > +       list_for_each_entry_safe(vma, vn, &ggtt->vm.inactive_list, vm_link) {
> > +               struct drm_i915_gem_object *obj = vma->obj;
> >  
> > -                       WARN_ON(i915_vma_bind(vma, obj->cache_level,
> > -                                             PIN_UPDATE));
> > -                       ggtt_bound = true;
> > -               }
> > +               if (!i915_vma_unbind(vma))
> > +                       continue;
> >  
> > -               if (ggtt_bound)
> > -                       WARN_ON(i915_gem_object_set_to_gtt_domain(obj, false));
> > +               WARN_ON(i915_vma_bind(vma, obj->cache_level, PIN_UPDATE));
> > +               WARN_ON(i915_gem_object_set_to_gtt_domain(obj, false));
> 
> This gets called multiple times per an object for partial and rotated
> views, but that should not be our performance bottleneck.

It is however worth mentioning that rewriting the GTT is one of the pain
points for resume. A few GiB of WC writes is not free, so we have tried
hard not to rewrite it multiple times and to defer setup until use.
(With ppGTT, the GGTT is emptier so full-ppgtt should be a net win.)
-Chris