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

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