Re: [PATCH 02/10] drm/i915: Use insert_page for pwrite_fast

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

Hi,

On 22/12/15 06:20, 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).
>
> v2: Pin pages before starting pwrite, Combined duplicate loops (Chris)
>
> v3: Combined loops based on local patch by Chris (Chris)
>
> v4: Added i915 wrapper function for drm_mm_insert_node_in_range (Chris)
>
> v5: Renamed wrapper function for drm_mm_insert_node_in_range (Chris)
>
> v5: Added wrapper for drm_mm_remove_node() (Chris)
>
> v6: Added get_pages call before pinning the pages (Tvrtko)
> Added remove_mappable_node() wrapper for drm_mm_remove_node() (Chris)
>
> Signed-off-by: Ankitprasad Sharma <ankitprasad.r.sharma@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 94 +++++++++++++++++++++++++++++++----------
>   1 file changed, 72 insertions(+), 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index bf7f203..f11ec89 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -61,6 +61,23 @@ static bool cpu_write_needs_clflush(struct drm_i915_gem_object *obj)
>   	return obj->pin_display;
>   }
>
> +static int
> +insert_mappable_node(struct drm_i915_private *i915,
> +                     struct drm_mm_node *node)
> +{
> +	return drm_mm_insert_node_in_range_generic(&i915->gtt.base.mm, node,
> +						   PAGE_SIZE, 0, 0,

It does not look ideal that the function name is saying it will insert a 
node and then it only inserts one page.

In that respect previous version looked better to me but since it is 
static and single use - whatever - this has been dragging for too long.

> +						   0, i915->gtt.mappable_end,
> +						   DRM_MM_SEARCH_DEFAULT,
> +						   DRM_MM_CREATE_DEFAULT);
> +}
> +
> +static void
> +remove_mappable_node(struct drm_mm_node *node)
> +{
> +	drm_mm_remove_node(node);
> +}
> +
>   /* some bookkeeping */
>   static void i915_gem_info_add_obj(struct drm_i915_private *dev_priv,
>   				  size_t size)
> @@ -760,20 +777,34 @@ fast_user_write(struct io_mapping *mapping,
>    * user into the GTT, uncached.
>    */
>   static int
> -i915_gem_gtt_pwrite_fast(struct drm_device *dev,
> +i915_gem_gtt_pwrite_fast(struct drm_i915_private *i915,
>   			 struct drm_i915_gem_object *obj,
>   			 struct drm_i915_gem_pwrite *args,
>   			 struct drm_file *file)
>   {
> -	struct drm_i915_private *dev_priv = dev->dev_private;
> -	ssize_t remain;
> -	loff_t offset, page_base;
> +	struct drm_mm_node node;
> +	uint64_t remain, offset;
>   	char __user *user_data;
> -	int page_offset, page_length, ret;
> +	int ret;
>
>   	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE | PIN_NONBLOCK);
> -	if (ret)
> -		goto out;
> +	if (ret) {
> +		memset(&node, 0, sizeof(node));
> +		ret = insert_mappable_node(i915, &node);
> +		if (ret)
> +			goto out;
> +
> +		ret = i915_gem_object_get_pages(obj);
> +		if (ret) {
> +			remove_mappable_node(&node);
> +			goto out;
> +		}
> +
> +		i915_gem_object_pin_pages(obj);
> +	} else {
> +		node.start = i915_gem_obj_ggtt_offset(obj);
> +		node.allocated = false;
> +	}
>
>   	ret = i915_gem_object_set_to_gtt_domain(obj, true);
>   	if (ret)
> @@ -783,31 +814,39 @@ i915_gem_gtt_pwrite_fast(struct drm_device *dev,
>   	if (ret)
>   		goto out_unpin;
>
> -	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);
> +	obj->dirty = true;
>
> -	while (remain > 0) {
> +	user_data = to_user_ptr(args->data_ptr);
> +	offset = args->offset;
> +	remain = args->size;
> +	while (remain) {
>   		/* Operation in this page
>   		 *
>   		 * page_base = page offset within aperture
>   		 * page_offset = offset within page
>   		 * page_length = bytes to copy for this 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;
> -
> +		u32 page_base = node.start;

Compiler does not complain about possible truncation here? I would 
change it to a type of equivalent width just in case. Even before it was 
loff_t.

> +		unsigned page_offset = offset_in_page(offset);
> +		unsigned page_length = PAGE_SIZE - page_offset;
> +		page_length = remain < page_length ? remain : page_length;
> +		if (node.allocated) {
> +			wmb();
> +			i915->gtt.base.insert_page(&i915->gtt.base,
> +						   i915_gem_object_get_dma_address(obj, offset >> PAGE_SHIFT),
> +						   node.start,
> +						   I915_CACHE_NONE,
> +						   0);
> +			wmb();
> +		} else {
> +			page_base += offset & PAGE_MASK;
> +		}
>   		/* 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,
> +		if (fast_user_write(i915->gtt.mappable, page_base,
>   				    page_offset, user_data, page_length)) {
>   			ret = -EFAULT;
>   			goto out_flush;
> @@ -821,7 +860,18 @@ i915_gem_gtt_pwrite_fast(struct drm_device *dev,
>   out_flush:
>   	intel_fb_obj_flush(obj, false, ORIGIN_GTT);
>   out_unpin:
> -	i915_gem_object_ggtt_unpin(obj);
> +	if (node.allocated) {
> +		wmb();
> +		i915->gtt.base.clear_range(&i915->gtt.base,
> +				node.start, node.size,
> +				true);
> +		remove_mappable_node(&node);
> +		i915_gem_object_unpin_pages(obj);
> +		i915_gem_object_put_pages(obj);
> +	}
> +	else {
> +		i915_gem_object_ggtt_unpin(obj);
> +	}
>   out:
>   	return ret;
>   }
> @@ -1086,7 +1136,7 @@ i915_gem_pwrite_ioctl(struct drm_device *dev, void *data,
>   	if (obj->tiling_mode == I915_TILING_NONE &&
>   	    obj->base.write_domain != I915_GEM_DOMAIN_CPU &&
>   	    cpu_write_needs_clflush(obj)) {
> -		ret = i915_gem_gtt_pwrite_fast(dev, obj, args, file);
> +		ret = i915_gem_gtt_pwrite_fast(dev_priv, obj, args, file);
>   		/* Note that the gtt paths might fail with non-page-backed user
>   		 * pointers (e.g. gtt mappings when moving data between
>   		 * textures). Fallback to the shmem path in that case. */
>

Regards,

Tvrtko

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