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rbtree: Undo augmented trees performance damage and regression
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Reimplement augmented RB-trees without sprinkling extra branches
all over the RB-tree code (which lives in the scheduler hot path).

This approach is 'borrowed' from Fabio's BFQ implementation and
relies on traversing the rebalance path after the RB-tree-op to
correct the heap property for insertion/removal and make up for
the damage done by the tree rotations.

For insertion the rebalance path is trivially that from the new
node upwards to the root, for removal it is that from the deepest
node in the path from the to be removed node that will still
be around after the removal.

[ This patch also fixes a video driver regression reported by
  Ali Gholami Rudi - the memtype->subtree_max_end was updated
  incorrectly. ]

Acked-by: Suresh Siddha <[email protected]>
Acked-by: Venkatesh Pallipadi <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Tested-by: Ali Gholami Rudi <[email protected]>
Cc: Fabio Checconi <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Linus Torvalds <[email protected]>
LKML-Reference: <1275414172.27810.27961.camel@twins>
Signed-off-by: Ingo Molnar <[email protected]>
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Peter Zijlstra authored and Ingo Molnar committed Jul 5, 2010
1 parent d596043 commit b945d6b
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Showing 3 changed files with 87 additions and 76 deletions.
34 changes: 6 additions & 28 deletions arch/x86/mm/pat_rbtree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -34,8 +34,7 @@
* memtype_lock protects the rbtree.
*/

static void memtype_rb_augment_cb(struct rb_node *node);
static struct rb_root memtype_rbroot = RB_AUGMENT_ROOT(&memtype_rb_augment_cb);
static struct rb_root memtype_rbroot = RB_ROOT;

static int is_node_overlap(struct memtype *node, u64 start, u64 end)
{
Expand All @@ -56,7 +55,7 @@ static u64 get_subtree_max_end(struct rb_node *node)
}

/* Update 'subtree_max_end' for a node, based on node and its children */
static void update_node_max_end(struct rb_node *node)
static void memtype_rb_augment_cb(struct rb_node *node, void *__unused)
{
struct memtype *data;
u64 max_end, child_max_end;
Expand All @@ -78,25 +77,6 @@ static void update_node_max_end(struct rb_node *node)
data->subtree_max_end = max_end;
}

/* Update 'subtree_max_end' for a node and all its ancestors */
static void update_path_max_end(struct rb_node *node)
{
u64 old_max_end, new_max_end;

while (node) {
struct memtype *data = container_of(node, struct memtype, rb);

old_max_end = data->subtree_max_end;
update_node_max_end(node);
new_max_end = data->subtree_max_end;

if (new_max_end == old_max_end)
break;

node = rb_parent(node);
}
}

/* Find the first (lowest start addr) overlapping range from rb tree */
static struct memtype *memtype_rb_lowest_match(struct rb_root *root,
u64 start, u64 end)
Expand Down Expand Up @@ -190,12 +170,6 @@ static int memtype_rb_check_conflict(struct rb_root *root,
return -EBUSY;
}

static void memtype_rb_augment_cb(struct rb_node *node)
{
if (node)
update_path_max_end(node);
}

static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)
{
struct rb_node **node = &(root->rb_node);
Expand All @@ -213,6 +187,7 @@ static void memtype_rb_insert(struct rb_root *root, struct memtype *newdata)

rb_link_node(&newdata->rb, parent, node);
rb_insert_color(&newdata->rb, root);
rb_augment_insert(&newdata->rb, memtype_rb_augment_cb, NULL);
}

int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)
Expand All @@ -234,13 +209,16 @@ int rbt_memtype_check_insert(struct memtype *new, unsigned long *ret_type)

struct memtype *rbt_memtype_erase(u64 start, u64 end)
{
struct rb_node *deepest;
struct memtype *data;

data = memtype_rb_exact_match(&memtype_rbroot, start, end);
if (!data)
goto out;

deepest = rb_augment_erase_begin(&data->rb);
rb_erase(&data->rb, &memtype_rbroot);
rb_augment_erase_end(deepest, memtype_rb_augment_cb, NULL);
out:
return data;
}
Expand Down
13 changes: 9 additions & 4 deletions include/linux/rbtree.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -110,7 +110,6 @@ struct rb_node
struct rb_root
{
struct rb_node *rb_node;
void (*augment_cb)(struct rb_node *node);
};


Expand All @@ -130,9 +129,7 @@ static inline void rb_set_color(struct rb_node *rb, int color)
rb->rb_parent_color = (rb->rb_parent_color & ~1) | color;
}

#define RB_ROOT (struct rb_root) { NULL, NULL, }
#define RB_AUGMENT_ROOT(x) (struct rb_root) { NULL, x}

#define RB_ROOT (struct rb_root) { NULL, }
#define rb_entry(ptr, type, member) container_of(ptr, type, member)

#define RB_EMPTY_ROOT(root) ((root)->rb_node == NULL)
Expand All @@ -142,6 +139,14 @@ static inline void rb_set_color(struct rb_node *rb, int color)
extern void rb_insert_color(struct rb_node *, struct rb_root *);
extern void rb_erase(struct rb_node *, struct rb_root *);

typedef void (*rb_augment_f)(struct rb_node *node, void *data);

extern void rb_augment_insert(struct rb_node *node,
rb_augment_f func, void *data);
extern struct rb_node *rb_augment_erase_begin(struct rb_node *node);
extern void rb_augment_erase_end(struct rb_node *node,
rb_augment_f func, void *data);

/* Find logical next and previous nodes in a tree */
extern struct rb_node *rb_next(const struct rb_node *);
extern struct rb_node *rb_prev(const struct rb_node *);
Expand Down
116 changes: 72 additions & 44 deletions lib/rbtree.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -44,11 +44,6 @@ static void __rb_rotate_left(struct rb_node *node, struct rb_root *root)
else
root->rb_node = right;
rb_set_parent(node, right);

if (root->augment_cb) {
root->augment_cb(node);
root->augment_cb(right);
}
}

static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
Expand All @@ -72,20 +67,12 @@ static void __rb_rotate_right(struct rb_node *node, struct rb_root *root)
else
root->rb_node = left;
rb_set_parent(node, left);

if (root->augment_cb) {
root->augment_cb(node);
root->augment_cb(left);
}
}

void rb_insert_color(struct rb_node *node, struct rb_root *root)
{
struct rb_node *parent, *gparent;

if (root->augment_cb)
root->augment_cb(node);

while ((parent = rb_parent(node)) && rb_is_red(parent))
{
gparent = rb_parent(parent);
Expand Down Expand Up @@ -240,15 +227,12 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
else
{
struct rb_node *old = node, *left;
int old_parent_cb = 0;
int successor_parent_cb = 0;

node = node->rb_right;
while ((left = node->rb_left) != NULL)
node = left;

if (rb_parent(old)) {
old_parent_cb = 1;
if (rb_parent(old)->rb_left == old)
rb_parent(old)->rb_left = node;
else
Expand All @@ -263,10 +247,8 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
if (parent == old) {
parent = node;
} else {
successor_parent_cb = 1;
if (child)
rb_set_parent(child, parent);

parent->rb_left = child;

node->rb_right = old->rb_right;
Expand All @@ -277,24 +259,6 @@ void rb_erase(struct rb_node *node, struct rb_root *root)
node->rb_left = old->rb_left;
rb_set_parent(old->rb_left, node);

if (root->augment_cb) {
/*
* Here, three different nodes can have new children.
* The parent of the successor node that was selected
* to replace the node to be erased.
* The node that is getting erased and is now replaced
* by its successor.
* The parent of the node getting erased-replaced.
*/
if (successor_parent_cb)
root->augment_cb(parent);

root->augment_cb(node);

if (old_parent_cb)
root->augment_cb(rb_parent(old));
}

goto color;
}

Expand All @@ -303,26 +267,90 @@ void rb_erase(struct rb_node *node, struct rb_root *root)

if (child)
rb_set_parent(child, parent);

if (parent) {
if (parent)
{
if (parent->rb_left == node)
parent->rb_left = child;
else
parent->rb_right = child;

if (root->augment_cb)
root->augment_cb(parent);

} else {
root->rb_node = child;
}
else
root->rb_node = child;

color:
if (color == RB_BLACK)
__rb_erase_color(child, parent, root);
}
EXPORT_SYMBOL(rb_erase);

static void rb_augment_path(struct rb_node *node, rb_augment_f func, void *data)
{
struct rb_node *parent;

up:
func(node, data);
parent = rb_parent(node);
if (!parent)
return;

if (node == parent->rb_left && parent->rb_right)
func(parent->rb_right, data);
else if (parent->rb_left)
func(parent->rb_left, data);

node = parent;
goto up;
}

/*
* after inserting @node into the tree, update the tree to account for
* both the new entry and any damage done by rebalance
*/
void rb_augment_insert(struct rb_node *node, rb_augment_f func, void *data)
{
if (node->rb_left)
node = node->rb_left;
else if (node->rb_right)
node = node->rb_right;

rb_augment_path(node, func, data);
}

/*
* before removing the node, find the deepest node on the rebalance path
* that will still be there after @node gets removed
*/
struct rb_node *rb_augment_erase_begin(struct rb_node *node)
{
struct rb_node *deepest;

if (!node->rb_right && !node->rb_left)
deepest = rb_parent(node);
else if (!node->rb_right)
deepest = node->rb_left;
else if (!node->rb_left)
deepest = node->rb_right;
else {
deepest = rb_next(node);
if (deepest->rb_right)
deepest = deepest->rb_right;
else if (rb_parent(deepest) != node)
deepest = rb_parent(deepest);
}

return deepest;
}

/*
* after removal, update the tree to account for the removed entry
* and any rebalance damage.
*/
void rb_augment_erase_end(struct rb_node *node, rb_augment_f func, void *data)
{
if (node)
rb_augment_path(node, func, data);
}

/*
* This function returns the first node (in sort order) of the tree.
*/
Expand Down

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