[PATCH 3/3] drm/mm: cleanup and improve next_hole_*_addr()

[Nirmoy]

Reviewed-by: Nirmoy Das <nirmoy.das at amd.com>

On 6/15/20 4:54 PM, Christian König wrote:
> Skipping just one branch of the tree is not the most
> effective approach.
>
> Instead use a macro to define the traversal functions and
> sort out both branch sides.
>
> This improves the performance of the unit tests by
> a factor of more than 4.
>
> Signed-off-by: Christian König <christian.koenig at amd.com>
> ---
>   drivers/gpu/drm/drm_mm.c | 106 +++++++++++++--------------------------
>   1 file changed, 34 insertions(+), 72 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
> index 177a5df0fe95..a4a04d246135 100644
> --- a/drivers/gpu/drm/drm_mm.c
> +++ b/drivers/gpu/drm/drm_mm.c
> @@ -325,6 +325,11 @@ static struct drm_mm_node *best_hole(struct drm_mm *mm, u64 size)
>   	return best;
>   }
>   
> +static bool usable_hole_addr(struct rb_node *rb, u64 size)
> +{
> +	return rb && rb_hole_addr_to_node(rb)->subtree_max_hole >= size;
> +}
> +
>   static struct drm_mm_node *find_hole_addr(struct drm_mm *mm, u64 addr, u64 size)
>   {
>   	struct rb_node *rb = mm->holes_addr.rb_node;
> @@ -333,7 +338,7 @@ static struct drm_mm_node *find_hole_addr(struct drm_mm *mm, u64 addr, u64 size)
>   	while (rb) {
>   		u64 hole_start;
>   
> -		if (rb_hole_addr_to_node(rb)->subtree_max_hole < size)
> +		if (!usable_hole_addr(rb, size))
>   			break;
>   
>   		node = rb_hole_addr_to_node(rb);
> @@ -374,82 +379,39 @@ first_hole(struct drm_mm *mm,
>   }
>   
>   /**
> - * next_hole_high_addr - returns next hole for a DRM_MM_INSERT_HIGH mode request
> - * @entry: previously selected drm_mm_node
> - * @size: size of the a hole needed for the request
> - *
> - * This function will verify whether left subtree of @entry has hole big enough
> - * to fit the requtested size. If so, it will return previous node of @entry or
> - * else it will return parent node of @entry
> + * DECLARE_NEXT_HOLE_ADDR - macro to declare next hole functions
> + * @name: name of function to declare
> + * @first: first rb member to traverse (either rb_left or rb_right).
> + * @last: last rb member to traverse (either rb_right or rb_left).
>    *
> - * It will also skip the complete left subtree if subtree_max_hole of that
> - * subtree is same as the subtree_max_hole of the @entry.
> - *
> - * Returns:
> - * previous node of @entry if left subtree of @entry can serve the request or
> - * else return parent of @entry
> + * This macro declares a function to return the next hole of the addr rb tree.
> + * While traversing the tree we take the searched size into account and only
> + * visit branches with potential big enough holes.
>    */
> -static struct drm_mm_node *
> -next_hole_high_addr(struct drm_mm_node *entry, u64 size)
> -{
> -	struct rb_node *rb_node, *left_rb_node, *parent_rb_node;
> -	struct drm_mm_node *left_node;
> -
> -	if (!entry)
> -		return NULL;
>   
> -	rb_node = &entry->rb_hole_addr;
> -	if (rb_node->rb_left) {
> -		left_rb_node = rb_node->rb_left;
> -		parent_rb_node = rb_parent(rb_node);
> -		left_node = rb_entry(left_rb_node,
> -				     struct drm_mm_node, rb_hole_addr);
> -		if (left_node->subtree_max_hole < size &&
> -		    parent_rb_node && parent_rb_node->rb_left != rb_node)
> -			return rb_hole_addr_to_node(parent_rb_node);
> -	}
> -
> -	return rb_hole_addr_to_node(rb_prev(rb_node));
> +#define DECLARE_NEXT_HOLE_ADDR(name, first, last)			\
> +static struct drm_mm_node *name(struct drm_mm_node *entry, u64 size)	\
> +{									\
> +	struct rb_node *parent, *node = &entry->rb_hole_addr;		\
> +									\
> +	if (!entry || RB_EMPTY_NODE(node))				\
> +		return NULL;						\
> +									\
> +	if (usable_hole_addr(node->first, size)) {			\
> +		node = node->first;					\
> +		while (usable_hole_addr(node->last, size))		\
> +			node = node->last;				\
> +		return rb_hole_addr_to_node(node);			\
> +	}								\
> +									\
> +	while ((parent = rb_parent(node)) && node == parent->first)	\
> +		node = parent;						\
> +									\
> +	return rb_hole_addr_to_node(parent);				\
>   }
>   
> -/**
> - * next_hole_low_addr - returns next hole for a DRM_MM_INSERT_LOW mode request
> - * @entry: previously selected drm_mm_node
> - * @size: size of the a hole needed for the request
> - *
> - * This function will verify whether right subtree of @entry has hole big enough
> - * to fit the requtested size. If so, it will return next node of @entry or
> - * else it will return parent node of @entry
> - *
> - * It will also skip the complete right subtree if subtree_max_hole of that
> - * subtree is same as the subtree_max_hole of the @entry.
> - *
> - * Returns:
> - * next node of @entry if right subtree of @entry can serve the request or
> - * else return parent of @entry
> - */
> -static struct drm_mm_node *
> -next_hole_low_addr(struct drm_mm_node *entry, u64 size)
> -{
> -	struct rb_node *rb_node, *right_rb_node, *parent_rb_node;
> -	struct drm_mm_node *right_node;
> -
> -	if (!entry)
> -		return NULL;
> -
> -	rb_node = &entry->rb_hole_addr;
> -	if (rb_node->rb_right) {
> -		right_rb_node = rb_node->rb_right;
> -		parent_rb_node = rb_parent(rb_node);
> -		right_node = rb_entry(right_rb_node,
> -				      struct drm_mm_node, rb_hole_addr);
> -		if (right_node->subtree_max_hole < size &&
> -		    parent_rb_node && parent_rb_node->rb_right != rb_node)
> -			return rb_hole_addr_to_node(parent_rb_node);
> -	}
> -
> -	return rb_hole_addr_to_node(rb_next(rb_node));
> -}
> +DECLARE_NEXT_HOLE_ADDR(next_hole_high_addr, rb_left, rb_right)
> +DECLARE_NEXT_HOLE_ADDR(next_hole_low_addr, rb_right, rb_left)
>   
>   static struct drm_mm_node *
>   next_hole(struct drm_mm *mm,