Re: [PATCH v2 5/5] drm/i915: Use partial view in mmap fault handler

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

On 04/30/2015 12:21 PM, Joonas Lahtinen wrote:
>
> Use partial view for huge BOs (bigger than the mappable aperture)
> in fault handler so that they can be accessed without trying to make
> room for them by evicting other objects.
>
> v2:
> - Only use partial views in the case where early rejection was
>    previously done.
> - Account variable type changes from previous reroll.
>
> Cc: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>   drivers/gpu/drm/i915/i915_gem.c | 69 +++++++++++++++++++++++++++--------------
>   1 file changed, 46 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index a020836..2f3fa0b 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -1635,6 +1635,7 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>   	struct drm_i915_gem_object *obj = to_intel_bo(vma->vm_private_data);
>   	struct drm_device *dev = obj->base.dev;
>   	struct drm_i915_private *dev_priv = dev->dev_private;
> +	struct i915_ggtt_view view = i915_ggtt_view_normal;
>   	pgoff_t page_offset;
>   	unsigned long pfn;
>   	int ret = 0;
> @@ -1667,8 +1668,21 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>   		goto unlock;
>   	}
>
> -	/* Now bind it into the GTT if needed */
> -	ret = i915_gem_obj_ggtt_pin(obj, 0, PIN_MAPPABLE);
> +	/* Use a partial view if the object is bigger than the aperture. */
> +	if (obj->base.size >= dev_priv->gtt.mappable_end) {
> +		static const unsigned int chunk_size = 256; // 1 MiB
> +		memset(&view, 0, sizeof(view));
> +		view.type = I915_GGTT_VIEW_PARTIAL;
> +		view.params.partial.offset = rounddown(page_offset, chunk_size);
> +		view.params.partial.size =
> +			min_t(unsigned int,
> +			      chunk_size,
> +			      (vma->vm_end - vma->vm_start)/PAGE_SIZE -
> +			      view.params.partial.offset);
> +	}
> +
> +	/* Now pin it into the GTT if needed */
> +	ret = i915_gem_object_ggtt_pin(obj, &view, 0, PIN_MAPPABLE);
>   	if (ret)
>   		goto unlock;
>
> @@ -1681,30 +1695,44 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>   		goto unpin;
>
>   	/* Finally, remap it using the new GTT offset */
> -	pfn = dev_priv->gtt.mappable_base + i915_gem_obj_ggtt_offset(obj);
> +	pfn = dev_priv->gtt.mappable_base +
> +		i915_gem_obj_ggtt_offset_view(obj, &view);
>   	pfn >>= PAGE_SHIFT;
>
> -	if (!obj->fault_mappable) {
> -		unsigned long size = min_t(unsigned long,
> -					   vma->vm_end - vma->vm_start,
> -					   obj->base.size);
> -		int i;
> +	if (unlikely(view.type == I915_GGTT_VIEW_PARTIAL)) {
> +		unsigned long base = vma->vm_start +
> +			(view.params.partial.offset << PAGE_SHIFT);
> +		unsigned int i;
>
> -		for (i = 0; i < size >> PAGE_SHIFT; i++) {
> -			ret = vm_insert_pfn(vma,
> -					    (unsigned long)vma->vm_start + i * PAGE_SIZE,
> -					    pfn + i);
> +		for (i = 0; i < view.params.partial.size; i++) {
> +			ret = vm_insert_pfn(vma, base + i * PAGE_SIZE, pfn + i);
>   			if (ret)
>   				break;
>   		}
> -
>   		obj->fault_mappable = true;
> -	} else
> -		ret = vm_insert_pfn(vma,
> -				    (unsigned long)vmf->virtual_address,
> -				    pfn + page_offset);

If I read the diff correctly you don't have equivalent handling (as the 
normal view) for when the case when the pre-fault fails somewhere in the 
middle?

That means if that happens you'll call vm_insert_pfn on the whole range 
again - is that OK?

Regards,

Tvrtko
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