drm: Track drm_mm nodes with an interval tree

In addition to the last-in/first-out stack for accessing drm_mm nodes,
we occasionally and in the future often want to find a drm_mm_node by an
address. To do so efficiently we need to track the nodes in an interval
tree - lookups for a particular address will then be O(lg(N)), where N
is the number of nodes in the range manager as opposed to O(N).
Insertion however gains an extra O(lg(N)) step for all nodes
irrespective of whether the interval tree is in use. For future i915
patches, eliminating the linear walk is a significant improvement.

v2: Use generic interval-tree template for u64 and faster insertion.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1470236651-678-1-git-send-email-chris@chris-wilson.co.uk

1 files changed, 110 insertions, 23 deletions

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index cb39f45..5c188c5 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -46,6 +46,7 @@
 #include <linux/slab.h>
 #include <linux/seq_file.h>
 #include <linux/export.h>
+#include <linux/interval_tree_generic.h>
 
 /**
  * DOC: Overview
@@ -103,6 +104,72 @@ static struct drm_mm_node *drm_mm_search_free_in_range_generic(const struct drm_
 						u64 end,
 						enum drm_mm_search_flags flags);
 
+#define START(node) ((node)->start)
+#define LAST(node)  ((node)->start + (node)->size - 1)
+
+INTERVAL_TREE_DEFINE(struct drm_mm_node, rb,
+		     u64, __subtree_last,
+		     START, LAST, static inline, drm_mm_interval_tree)
+
+struct drm_mm_node *
+drm_mm_interval_first(struct drm_mm *mm, u64 start, u64 last)
+{
+	return drm_mm_interval_tree_iter_first(&mm->interval_tree,
+					       start, last);
+}
+EXPORT_SYMBOL(drm_mm_interval_first);
+
+struct drm_mm_node *
+drm_mm_interval_next(struct drm_mm_node *node, u64 start, u64 last)
+{
+	return drm_mm_interval_tree_iter_next(node, start, last);
+}
+EXPORT_SYMBOL(drm_mm_interval_next);
+
+static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
+					  struct drm_mm_node *node)
+{
+	struct drm_mm *mm = hole_node->mm;
+	struct rb_node **link, *rb;
+	struct drm_mm_node *parent;
+
+	node->__subtree_last = LAST(node);
+
+	if (hole_node->allocated) {
+		rb = &hole_node->rb;
+		while (rb) {
+			parent = rb_entry(rb, struct drm_mm_node, rb);
+			if (parent->__subtree_last >= node->__subtree_last)
+				break;
+
+			parent->__subtree_last = node->__subtree_last;
+			rb = rb_parent(rb);
+		}
+
+		rb = &hole_node->rb;
+		link = &hole_node->rb.rb_right;
+	} else {
+		rb = NULL;
+		link = &mm->interval_tree.rb_node;
+	}
+
+	while (*link) {
+		rb = *link;
+		parent = rb_entry(rb, struct drm_mm_node, rb);
+		if (parent->__subtree_last < node->__subtree_last)
+			parent->__subtree_last = node->__subtree_last;
+		if (node->start < parent->start)
+			link = &parent->rb.rb_left;
+		else
+			link = &parent->rb.rb_right;
+	}
+
+	rb_link_node(&node->rb, rb, link);
+	rb_insert_augmented(&node->rb,
+			    &mm->interval_tree,
+			    &drm_mm_interval_tree_augment);
+}
+
 static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
 				 struct drm_mm_node *node,
 				 u64 size, unsigned alignment,
@@ -153,6 +220,8 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
 	INIT_LIST_HEAD(&node->hole_stack);
 	list_add(&node->node_list, &hole_node->node_list);
 
+	drm_mm_interval_tree_add_node(hole_node, node);
+
 	BUG_ON(node->start + node->size > adj_end);
 
 	node->hole_follows = 0;
@@ -178,41 +247,52 @@ static void drm_mm_insert_helper(struct drm_mm_node *hole_node,
  */
 int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
 {
+	u64 end = node->start + node->size;
 	struct drm_mm_node *hole;
-	u64 end;
-	u64 hole_start;
-	u64 hole_end;
-
-	BUG_ON(node == NULL);
+	u64 hole_start, hole_end;
 
 	end = node->start + node->size;
 
 	/* Find the relevant hole to add our node to */
-	drm_mm_for_each_hole(hole, mm, hole_start, hole_end) {
-		if (hole_start > node->start || hole_end < end)
-			continue;
+	hole = drm_mm_interval_tree_iter_first(&mm->interval_tree,
+					       node->start, ~(u64)0);
+	if (hole) {
+		if (hole->start < end)
+			return -ENOSPC;
+	} else {
+		hole = list_entry(&mm->head_node.node_list,
+				  typeof(*hole), node_list);
+	}
 
-		node->mm = mm;
-		node->allocated = 1;
+	hole = list_last_entry(&hole->node_list, typeof(*hole), node_list);
+	if (!hole->hole_follows)
+		return -ENOSPC;
 
-		INIT_LIST_HEAD(&node->hole_stack);
-		list_add(&node->node_list, &hole->node_list);
+	hole_start = __drm_mm_hole_node_start(hole);
+	hole_end = __drm_mm_hole_node_end(hole);
+	if (hole_start > node->start || hole_end < end)
+		return -ENOSPC;
 
-		if (node->start == hole_start) {
-			hole->hole_follows = 0;
-			list_del_init(&hole->hole_stack);
-		}
+	node->mm = mm;
+	node->allocated = 1;
 
-		node->hole_follows = 0;
-		if (end != hole_end) {
-			list_add(&node->hole_stack, &mm->hole_stack);
-			node->hole_follows = 1;
-		}
+	INIT_LIST_HEAD(&node->hole_stack);
+	list_add(&node->node_list, &hole->node_list);
 
-		return 0;
+	drm_mm_interval_tree_add_node(hole, node);
+
+	if (node->start == hole_start) {
+		hole->hole_follows = 0;
+		list_del_init(&hole->hole_stack);
+	}
+
+	node->hole_follows = 0;
+	if (end != hole_end) {
+		list_add(&node->hole_stack, &mm->hole_stack);
+		node->hole_follows = 1;
 	}
 
-	return -ENOSPC;
+	return 0;
 }
 EXPORT_SYMBOL(drm_mm_reserve_node);
 
@@ -302,6 +382,8 @@ static void drm_mm_insert_helper_range(struct drm_mm_node *hole_node,
 	INIT_LIST_HEAD(&node->hole_stack);
 	list_add(&node->node_list, &hole_node->node_list);
 
+	drm_mm_interval_tree_add_node(hole_node, node);
+
 	BUG_ON(node->start < start);
 	BUG_ON(node->start < adj_start);
 	BUG_ON(node->start + node->size > adj_end);
@@ -390,6 +472,7 @@ void drm_mm_remove_node(struct drm_mm_node *node)
 	} else
 		list_move(&prev_node->hole_stack, &mm->hole_stack);
 
+	drm_mm_interval_tree_remove(node, &mm->interval_tree);
 	list_del(&node->node_list);
 	node->allocated = 0;
 }
@@ -516,11 +599,13 @@ void drm_mm_replace_node(struct drm_mm_node *old, struct drm_mm_node *new)
 {
 	list_replace(&old->node_list, &new->node_list);
 	list_replace(&old->hole_stack, &new->hole_stack);
+	rb_replace_node(&old->rb, &new->rb, &old->mm->interval_tree);
 	new->hole_follows = old->hole_follows;
 	new->mm = old->mm;
 	new->start = old->start;
 	new->size = old->size;
 	new->color = old->color;
+	new->__subtree_last = old->__subtree_last;
 
 	old->allocated = 0;
 	new->allocated = 1;
@@ -758,6 +843,8 @@ void drm_mm_init(struct drm_mm * mm, u64 start, u64 size)
 	mm->head_node.size = start - mm->head_node.start;
 	list_add_tail(&mm->head_node.hole_stack, &mm->hole_stack);
 
+	mm->interval_tree = RB_ROOT;
+
 	mm->color_adjust = NULL;
 }
 EXPORT_SYMBOL(drm_mm_init);