Re: [PATCH 3/3] drm/i915: Use insert_page for pwrite_fast

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, Nov 05, 2015 at 05:15:59PM +0530, ankitprasad.r.sharma@intel.com wrote:
> From: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> 
> In pwrite_fast, map an object page by page if obj_ggtt_pin fails. First,
> we try a nonblocking pin for the whole object (since that is fastest if
> reused), then failing that we try to grab one page in the mappable
> aperture. It also allows us to handle objects larger than the mappable
> aperture (e.g. if we need to pwrite with vGPU restricting the aperture
> to a measely 8MiB or something like that).

We already have a fallback to the shmem pwrite. Why do we need this?
-Daniel

> 
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 92 ++++++++++++++++++++++++++++++-----------
>  1 file changed, 69 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index bf5ef7a..9132240 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -766,14 +766,26 @@ i915_gem_gtt_pwrite_fast(struct drm_device *dev,
>  			 struct drm_file *file)
>  {
>  	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct drm_mm_node node;
>  	ssize_t remain;
>  	loff_t offset, page_base;
>  	char __user *user_data;
> -	int page_offset, page_length, ret;
> +	int page_offset, page_length, ret, i;
> +	bool pinned = true;
>  
>  	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE | PIN_NONBLOCK);
> -	if (ret)
> -		goto out;
> +	if (ret) {
> +		pinned = false;
> +		memset(&node, 0, sizeof(node));
> +		ret = drm_mm_insert_node_in_range_generic(&dev_priv->gtt.base.mm,
> +							  &node, 4096, 0,
> +							  I915_CACHE_NONE, 0,
> +							  dev_priv->gtt.mappable_end,
> +							  DRM_MM_SEARCH_DEFAULT,
> +							  DRM_MM_CREATE_DEFAULT);
> +		if (ret)
> +			goto out;
> +	}
>  
>  	ret = i915_gem_object_set_to_gtt_domain(obj, true);
>  	if (ret)
> @@ -786,42 +798,76 @@ i915_gem_gtt_pwrite_fast(struct drm_device *dev,
>  	user_data = to_user_ptr(args->data_ptr);
>  	remain = args->size;
>  
> -	offset = i915_gem_obj_ggtt_offset(obj) + args->offset;
> -
>  	intel_fb_obj_invalidate(obj, ORIGIN_GTT);
>  
> -	while (remain > 0) {
> -		/* Operation in this page
> +	if (likely(pinned)) {
> +		offset = i915_gem_obj_ggtt_offset(obj) + args->offset;
> +		/* Operation in the page
>  		 *
>  		 * page_base = page offset within aperture
>  		 * page_offset = offset within page
> -		 * page_length = bytes to copy for this page
> +		 * page_length = bytes to copy for the page
>  		 */
>  		page_base = offset & PAGE_MASK;
>  		page_offset = offset_in_page(offset);
> -		page_length = remain;
> -		if ((page_offset + remain) > PAGE_SIZE)
> -			page_length = PAGE_SIZE - page_offset;
> +		while (remain > 0) {
> +			page_length = remain;
> +			if ((page_offset + remain) > PAGE_SIZE)
> +				page_length = PAGE_SIZE - page_offset;
> +
> +			/* If we get a fault while copying data, then (presumably) our
> +			 * source page isn't available.  Return the error and we'll
> +			 * retry in the slow path.
> +			 */
> +			if (fast_user_write(dev_priv->gtt.mappable, page_base,
> +						page_offset, user_data, page_length)) {
> +				ret = -EFAULT;
> +				goto out_flush;
> +			}
>  
> -		/* If we get a fault while copying data, then (presumably) our
> -		 * source page isn't available.  Return the error and we'll
> -		 * retry in the slow path.
> -		 */
> -		if (fast_user_write(dev_priv->gtt.mappable, page_base,
> -				    page_offset, user_data, page_length)) {
> -			ret = -EFAULT;
> -			goto out_flush;
> +			remain -= page_length;
> +			user_data += page_length;
> +			page_offset = 0;
>  		}
> +	} else {
> +		i = args->offset / PAGE_SIZE;
> +		page_offset = offset_in_page(args->offset);
> +		while (remain > 0) {
> +			page_length = remain;
> +			if ((page_offset + remain) > PAGE_SIZE)
> +				page_length = PAGE_SIZE - page_offset;
> +
> +			wmb();
> +			dev_priv->gtt.base.insert_page(&dev_priv->gtt.base,
> +					i915_gem_object_get_dma_address(obj, i),
> +					node.start,
> +					I915_CACHE_NONE,
> +					0);
> +			wmb();
> +
> +			if (fast_user_write(dev_priv->gtt.mappable, node.start,
> +						page_offset, user_data, page_length)) {
> +				ret = -EFAULT;
> +				goto out_flush;
> +			}
>  
> -		remain -= page_length;
> -		user_data += page_length;
> -		offset += page_length;
> +			remain -= page_length;
> +			user_data += page_length;
> +			page_offset = 0;
> +			i++;
> +		}
> +		wmb();
> +		dev_priv->gtt.base.clear_range(&dev_priv->gtt.base,
> +				node.start, node.size,
> +				true);
> +		drm_mm_remove_node(&node);
>  	}
>  
>  out_flush:
>  	intel_fb_obj_flush(obj, false, ORIGIN_GTT);
>  out_unpin:
> -	i915_gem_object_ggtt_unpin(obj);
> +	if (pinned)
> +		i915_gem_object_ggtt_unpin(obj);
>  out:
>  	return ret;
>  }
> -- 
> 1.9.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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