Re: [PATCH 2/6] drm/i915: Provide a cheap ggtt vma lookup

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Sep 24, 2013 at 09:57:57AM -0700, Ben Widawsky wrote:
> "We do fairly often lookup the ggtt vma for an obj." - Chris Wilson. As
> such, provide a function to offer slightly cheaper access to the vma.
> Not performance tested. By my quick estimation it saves at least 3
> pointer dereferences from the existing mechanism.
> 
> This patch mostly matches code from Chris in
> <20130911221430.GB7825@nuc-i3427.alporthouse.com>
> 
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> ---
>  drivers/gpu/drm/i915/i915_drv.h |  4 +++-
>  drivers/gpu/drm/i915/i915_gem.c | 17 +++++++++++++++--
>  2 files changed, 18 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 07de53c..67a31c2 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2026,6 +2026,9 @@ struct i915_vma *i915_gem_obj_to_vma(struct drm_i915_gem_object *obj,
>  struct i915_vma *
>  i915_gem_obj_lookup_or_create_vma(struct drm_i915_gem_object *obj,
>  				  struct i915_address_space *vm);
> +
> +struct i915_vma *i915_gem_obj_to_ggtt(struct drm_i915_gem_object *obj);
> +
>  /* Some GGTT VM helpers */
>  #define obj_to_ggtt(obj) \
>  	(&((struct drm_i915_private *)(obj)->base.dev->dev_private)->gtt.base)
> @@ -2062,7 +2065,6 @@ i915_gem_obj_ggtt_pin(struct drm_i915_gem_object *obj,
>  	return i915_gem_object_pin(obj, obj_to_ggtt(obj), alignment,
>  				   map_and_fenceable, nonblocking);
>  }
> -#undef obj_to_ggtt

Bikeshed police: obj_to_gtt should probably be a static inline function
and also might need a bit a prefix now ...
-Daniel

>  
>  /* i915_gem_context.c */
>  void i915_gem_context_init(struct drm_device *dev);
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 8450724..6b134f0 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3403,8 +3403,7 @@ i915_gem_object_set_to_gtt_domain(struct drm_i915_gem_object *obj, bool write)
>  
>  	/* And bump the LRU for this access */
>  	if (i915_gem_object_is_inactive(obj)) {
> -		struct i915_vma *vma = i915_gem_obj_to_vma(obj,
> -							   &dev_priv->gtt.base);
> +		struct i915_vma *vma = i915_gem_obj_to_ggtt(obj);
>  		if (vma)
>  			list_move_tail(&vma->mm_list,
>  				       &dev_priv->gtt.base.inactive_list);
> @@ -4940,3 +4939,17 @@ unsigned long i915_gem_obj_size(struct drm_i915_gem_object *o,
>  
>  	return 0;
>  }
> +
> +struct i915_vma *i915_gem_obj_to_ggtt(struct drm_i915_gem_object *obj)
> +{
> +	struct i915_vma *vma;
> +
> +	if (WARN_ON(list_empty(&obj->vma_list)))
> +		return NULL;
> +
> +	vma = list_first_entry(&obj->vma_list, typeof(*vma), vma_link);
> +	if (WARN_ON(vma->vm != obj_to_ggtt(obj)))
> +		return NULL;
> +
> +	return vma;
> +}
> -- 
> 1.8.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch