Re: [PATCH 04/18] drm/i915: Avoid clearing preallocated regions from the GTT

[Ben Widawsky <ben@bwidawsk.net>]

On Fri, 19 Oct 2012 18:03:10 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |    2 ++
>  drivers/gpu/drm/i915/i915_gem_gtt.c |   35 ++++++++++++++++++++++++++++++++---
>  2 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 687f379..589b2f3 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -908,6 +908,8 @@ enum i915_cache_level {
>  	I915_CACHE_LLC_MLC, /* gen6+, in docs at least! */
>  };
>  
> +#define I915_GTT_RESERVED ((struct drm_mm_node *)0x1)
> +
>  struct drm_i915_gem_object_ops {
>  	/* Interface between the GEM object and its backing storage.
>  	 * get_pages() is called once prior to the use of the associated set
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 47e427e..d9d3fc7 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -378,18 +378,47 @@ void i915_gem_init_global_gtt(struct drm_device *dev,
>  			      unsigned long end)
>  {
>  	drm_i915_private_t *dev_priv = dev->dev_private;
> +	struct drm_mm_node *entry;
> +	struct drm_i915_gem_object *obj;
>  
> -	/* Substract the guard page ... */
> +	/* Subtract the guard page ... */
>  	drm_mm_init(&dev_priv->mm.gtt_space, start, end - start - PAGE_SIZE);
>  	if (!HAS_LLC(dev))
>  		dev_priv->mm.gtt_space.color_adjust = i915_gtt_color_adjust;
>  
> +	/* Mark any preallocated objects as occupied */
> +	list_for_each_entry(obj, &dev_priv->mm.bound_list, gtt_list) {
> +		DRM_DEBUG_KMS("reserving preallocated space: %x + %zx\n",
> +			      obj->gtt_offset, obj->base.size);
> +
> +		BUG_ON(obj->gtt_space != I915_GTT_RESERVED);
> +		obj->gtt_space = drm_mm_create_block(&dev_priv->mm.gtt_space,
> +						     obj->gtt_offset,
> +						     obj->base.size,
> +						     false);
> +		obj->has_global_gtt_mapping = 1;
> +	}
> +

I think this requires more explanation. I believe on driver init the
bound_list should be empty. What am I missing? If this is for some
future thing where you're going to bind objects before we init the gtt,
a comment in the commit message would have been really terrific.

>  	dev_priv->mm.gtt_start = start;
>  	dev_priv->mm.gtt_mappable_end = mappable_end;
>  	dev_priv->mm.gtt_end = end;
>  	dev_priv->mm.gtt_total = end - start;
>  	dev_priv->mm.mappable_gtt_total = min(end, mappable_end) - start;
>  
> -	/* ... but ensure that we clear the entire range. */
> -	intel_gtt_clear_range(start / PAGE_SIZE, (end-start) / PAGE_SIZE);
> +	/* Clear any non-preallocated blocks */
> +	list_for_each_entry(entry, &dev_priv->mm.gtt_space.hole_stack, hole_stack) {
> +		unsigned long hole_start = entry->start + entry->size;
> +		unsigned long hole_end = list_entry(entry->node_list.next,
> +						    struct drm_mm_node,
> +						    node_list)->start;
> +
> +		DRM_DEBUG_KMS("clearing unused GTT space: [%lx, %lx]\n",
> +			      hole_start, hole_end);
> +
> +		intel_gtt_clear_range(hole_start / PAGE_SIZE, +
> (hole_end-hole_start) / PAGE_SIZE); +	} + +	/* And finally clear the
> reserved guard page */ +	intel_gtt_clear_range(end / PAGE_SIZE -
> 1, 1); }

-- 
Ben Widawsky, Intel Open Source Technology Center