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

[Chris Wilson]

Quoting Chris Wilson (2018-06-05 09:19:07)
> 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.)

Hmm, we can filter on vma->flags & PIN_GLOBAL so that we don't touch
aliasing_ppgtt only vma...
-Chris