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

Ben Widawsky
2012-10-26T22:22:45Z

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