[PATCH 08/10] dma-buf/resv: replace shared fence with new fences container

[Chris Wilson]

Quoting Chris Wilson (2019-08-21 16:24:22)
> Quoting Christian König (2019-08-21 13:31:45)
> > @@ -117,17 +120,10 @@ i915_gem_busy_ioctl(struct drm_device *dev, void *data,
> >                 busy_check_writer(rcu_dereference(obj->base.resv->fence_excl));
> >  
> >         /* Translate shared fences to READ set of engines */
> > -       list = rcu_dereference(obj->base.resv->fence);
> > -       if (list) {
> > -               unsigned int shared_count = list->shared_count, i;
> > -
> > -               for (i = 0; i < shared_count; ++i) {
> > -                       struct dma_fence *fence =
> > -                               rcu_dereference(list->shared[i]);
> > -
> > -                       args->busy |= busy_check_reader(fence);
> > -               }
> > -       }
> > +       readers = dma_resv_fences_get_rcu(&obj->base.resv->readers);
> > +       dma_fence_array_for_each(fence, cursor, readers)
> > +               args->busy |= busy_check_reader(fence);
> > +       dma_fence_put(readers);
> 
> That's underwhelming, the full-mb shows up in scaling tests (I'll test
> the impact of this series later). Something like,

To put some numbers to it, adding the full-mb adds 5ns to a single
thread on Kabylake and 20ns under contention.
-Chris