Re: [PATCH 13/28] drm/i915: Avoid clearing preallocated regions from the GTT

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Apr 24, 2012 at 03:47:42PM +0100, Chris Wilson wrote:
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_drv.h     |    2 ++
>  drivers/gpu/drm/i915/i915_gem_gtt.c |   32 +++++++++++++++++++++++++++++---
>  2 files changed, 31 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 32e6c4d..3492e20 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -827,6 +827,8 @@ enum i915_cache_level {
>  	I915_CACHE_LLC_MLC, /* gen6+ */
>  };
>  
> +#define I915_GTT_RESERVED ((struct drm_mm_node *)0x1)
> +
>  struct drm_i915_gem_object {
>  	struct drm_gem_object base;
>  
> diff --git a/drivers/gpu/drm/i915/i915_gem_gtt.c b/drivers/gpu/drm/i915/i915_gem_gtt.c
> index 25c8bf9..b0c20a5 100644
> --- a/drivers/gpu/drm/i915/i915_gem_gtt.c
> +++ b/drivers/gpu/drm/i915/i915_gem_gtt.c
> @@ -417,16 +417,42 @@ 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);
>  
> +	/* Mark any preallocated objects as occupied */
> +	list_for_each_entry(obj, &dev_priv->mm.gtt_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;
> +	}
> +
>  	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);
> +	}

Assuming I'm reading the code correctly this does not clear the unmanaged
guard page at the end of the gtt.
-Daniel
-- 
Daniel Vetter
Mail: daniel@ffwll.ch
Mobile: +41 (0)79 365 57 48