Re: [PATCH 7/9] drm/vmwgfx: Use an RBtree instead of linked list for MOB resources

[Deepak Singh Rawat <drawat@vmware.com>]

Reviewed-by: Deepak Rawat <drawat@vmware.com>

On Fri, 2019-04-12 at 09:04 -0700, Thomas Hellstrom wrote:
> With emulated coherent memory we need to be able to quickly look up
> a resource from the MOB offset. Instead of traversing a linked list
> with
> O(n) worst case, use an RBtree with O(log n) worst case complexity.
> 
> Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
> ---
>  drivers/gpu/drm/vmwgfx/vmwgfx_bo.c       |  5 ++--
>  drivers/gpu/drm/vmwgfx/vmwgfx_drv.h      | 10 +++----
>  drivers/gpu/drm/vmwgfx/vmwgfx_resource.c | 33 +++++++++++++++++-----
> --
>  3 files changed, 32 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> index 90ca866640fe..e8bc7a7ac031 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_bo.c
> @@ -464,6 +464,7 @@ void vmw_bo_bo_free(struct ttm_buffer_object *bo)
>  	struct vmw_buffer_object *vmw_bo = vmw_buffer_object(bo);
>  
>  	WARN_ON(vmw_bo->dirty);
> +	WARN_ON(!RB_EMPTY_ROOT(&vmw_bo->res_tree));
>  	vmw_bo_unmap(vmw_bo);
>  	kfree(vmw_bo);
>  }
> @@ -480,6 +481,7 @@ static void vmw_user_bo_destroy(struct
> ttm_buffer_object *bo)
>  	struct vmw_buffer_object *vbo = &vmw_user_bo->vbo;
>  
>  	WARN_ON(vbo->dirty);
> +	WARN_ON(!RB_EMPTY_ROOT(&vbo->res_tree));
>  	vmw_bo_unmap(vbo);
>  	ttm_prime_object_kfree(vmw_user_bo, prime);
>  }
> @@ -515,8 +517,7 @@ int vmw_bo_init(struct vmw_private *dev_priv,
>  	memset(vmw_bo, 0, sizeof(*vmw_bo));
>  	BUILD_BUG_ON(TTM_MAX_BO_PRIORITY <= 3);
>  	vmw_bo->base.priority = 3;
> -
> -	INIT_LIST_HEAD(&vmw_bo->res_list);
> +	vmw_bo->res_tree = RB_ROOT;
>  
>  	ret = ttm_bo_init(bdev, &vmw_bo->base, size,
>  			  ttm_bo_type_device, placement,
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> index f05fce52fbb4..81ebcd668038 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.h
> @@ -90,7 +90,7 @@ struct vmw_fpriv {
>  /**
>   * struct vmw_buffer_object - TTM buffer object with vmwgfx
> additions
>   * @base: The TTM buffer object
> - * @res_list: List of resources using this buffer object as a
> backing MOB
> + * @res_tree: RB tree of resources using this buffer object as a
> backing MOB
>   * @pin_count: pin depth
>   * @dx_query_ctx: DX context if this buffer object is used as a DX
> query MOB
>   * @map: Kmap object for semi-persistent mappings
> @@ -99,7 +99,7 @@ struct vmw_fpriv {
>   */
>  struct vmw_buffer_object {
>  	struct ttm_buffer_object base;
> -	struct list_head res_list;
> +	struct rb_root res_tree;
>  	s32 pin_count;
>  	/* Not ref-counted.  Protected by binding_mutex */
>  	struct vmw_resource *dx_query_ctx;
> @@ -147,8 +147,8 @@ struct vmw_res_func;
>   * pin-count greater than zero. It is not on the resource LRU lists
> and its
>   * backup buffer is pinned. Hence it can't be evicted.
>   * @func: Method vtable for this resource. Immutable.
> + * @mob_node; Node for the MOB backup rbtree. Protected by @backup
> reserved.
>   * @lru_head: List head for the LRU list. Protected by
> @dev_priv::resource_lock.
> - * @mob_head: List head for the MOB backup list. Protected by
> @backup reserved.
>   * @binding_head: List head for the context binding list. Protected
> by
>   * the @dev_priv::binding_mutex
>   * @res_free: The resource destructor.
> @@ -169,8 +169,8 @@ struct vmw_resource {
>  	unsigned long backup_offset;
>  	unsigned long pin_count;
>  	const struct vmw_res_func *func;
> +	struct rb_node mob_node;
>  	struct list_head lru_head;
> -	struct list_head mob_head;
>  	struct list_head binding_head;
>  	struct vmw_resource_dirty *dirty;
>  	void (*res_free) (struct vmw_resource *res);
> @@ -743,7 +743,7 @@ void vmw_resource_dirty_update(struct
> vmw_resource *res, pgoff_t start,
>   */
>  static inline bool vmw_resource_mob_attached(const struct
> vmw_resource *res)
>  {
> -	return !list_empty(&res->mob_head);
> +	return !RB_EMPTY_NODE(&res->mob_node);
>  }
>  
>  /**
> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> b/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> index d35f4bd32cd9..ff9fe5650468 100644
> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_resource.c
> @@ -41,11 +41,24 @@
>  void vmw_resource_mob_attach(struct vmw_resource *res)
>  {
>  	struct vmw_buffer_object *backup = res->backup;
> +	struct rb_node **new = &backup->res_tree.rb_node, *parent =
> NULL;
>  
>  	lockdep_assert_held(&backup->base.resv->lock.base);
>  	res->used_prio = (res->res_dirty) ? res->func->dirty_prio :
>  		res->func->prio;
> -	list_add_tail(&res->mob_head, &backup->res_list);
> +
> +	while (*new) {
> +		struct vmw_resource *this =
> +			container_of(*new, struct vmw_resource,
> mob_node);
> +
> +		parent = *new;
> +		new = (res->backup_offset < this->backup_offset) ?
> +			&((*new)->rb_left) : &((*new)->rb_right);
> +	}
> +
> +	rb_link_node(&res->mob_node, parent, new);
> +	rb_insert_color(&res->mob_node, &backup->res_tree);
> +
>  	vmw_bo_prio_add(backup, res->used_prio);
>  }
>  
> @@ -59,7 +72,8 @@ void vmw_resource_mob_detach(struct vmw_resource
> *res)
>  
>  	lockdep_assert_held(&backup->base.resv->lock.base);
>  	if (vmw_resource_mob_attached(res)) {
> -		list_del_init(&res->mob_head);
> +		rb_erase(&res->mob_node, &backup->res_tree);
> +		RB_CLEAR_NODE(&res->mob_node);
>  		vmw_bo_prio_del(backup, res->used_prio);
>  	}
>  }
> @@ -206,8 +220,8 @@ int vmw_resource_init(struct vmw_private
> *dev_priv, struct vmw_resource *res,
>  	res->res_free = res_free;
>  	res->dev_priv = dev_priv;
>  	res->func = func;
> +	RB_CLEAR_NODE(&res->mob_node);
>  	INIT_LIST_HEAD(&res->lru_head);
> -	INIT_LIST_HEAD(&res->mob_head);
>  	INIT_LIST_HEAD(&res->binding_head);
>  	res->id = -1;
>  	res->backup = NULL;
> @@ -755,19 +769,20 @@ int vmw_resource_validate(struct vmw_resource
> *res, bool intr)
>   */
>  void vmw_resource_unbind_list(struct vmw_buffer_object *vbo)
>  {
> -
> -	struct vmw_resource *res, *next;
>  	struct ttm_validate_buffer val_buf = {
>  		.bo = &vbo->base,
>  		.num_shared = 0
>  	};
>  
>  	lockdep_assert_held(&vbo->base.resv->lock.base);
> -	list_for_each_entry_safe(res, next, &vbo->res_list, mob_head) {
> -		if (!res->func->unbind)
> -			continue;
> +	while (!RB_EMPTY_ROOT(&vbo->res_tree)) {
> +		struct rb_node *node = vbo->res_tree.rb_node;
> +		struct vmw_resource *res =
> +			container_of(node, struct vmw_resource,
> mob_node);
> +
> +		if (!WARN_ON_ONCE(!res->func->unbind))
> +			(void) res->func->unbind(res, res->res_dirty,
> &val_buf);
>  
> -		(void) res->func->unbind(res, res->res_dirty,
> &val_buf);
>  		res->backup_dirty = true;
>  		res->res_dirty = false;
>  		vmw_resource_mob_detach(res);
> -- 
> 2.20.1
>