Re: [PATCH 1/4] drm/i915: Drop wmb() inside pread_gtt

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Jul 18, 2019 at 03:54:04PM +0100, Chris Wilson wrote:
> Inside pread, we only ever read from the GTT so the serialising wmb()
> instructions around the GGTT PTE updates are pointless.

Hard to argue with that.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index a207b90924e4..fed0bc421a55 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -395,11 +395,9 @@ i915_gem_gtt_pread(struct drm_i915_gem_object *obj,
>  		unsigned page_length = PAGE_SIZE - page_offset;
>  		page_length = remain < page_length ? remain : page_length;
>  		if (node.allocated) {
> -			wmb();
>  			ggtt->vm.insert_page(&ggtt->vm,
>  					     i915_gem_object_get_dma_address(obj, offset >> PAGE_SHIFT),
>  					     node.start, I915_CACHE_NONE, 0);
> -			wmb();
>  		} else {
>  			page_base += offset & PAGE_MASK;
>  		}
> @@ -419,7 +417,6 @@ i915_gem_gtt_pread(struct drm_i915_gem_object *obj,
>  out_unpin:
>  	mutex_lock(&i915->drm.struct_mutex);
>  	if (node.allocated) {
> -		wmb();
>  		ggtt->vm.clear_range(&ggtt->vm, node.start, node.size);
>  		remove_mappable_node(&node);
>  	} else {
> -- 
> 2.22.0
> 
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-- 
Ville Syrjälä
Intel
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