rbtree: inline rb_first()

Patch series "rbree: inline rb_first() and rb_last()".

Inline these two small helpers, heavily used in TCP and FQ packet scheduler,
and in many other places.

This reduces kernel text size, and brings an 1.5 % improvement on network
TCP stress test.


This patch (of 2):

This is a very small function, inlining it saves cpu cycles by reducing
register pressure and removing call/ret overhead.

It also reduces vmlinux text size by 744 bytes on a typical x86_64 build.

Before:

size vmlinux
text data bss dec hex filename
34812525 22177365 5685248 62675138 3bc58c2 vmlinux

After:

size vmlinux
text data bss dec hex filename
34811781 22177365 5685248 62674394 3bc55da vmlinux

[[e-mail]: fix rust build]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Eric Dumazet <[e-mail]>
Signed-off-by: Miguel Ojeda <[e-mail]>
Reviewed-by: Kuan-Wei Chiu <[e-mail]>
Cc: Jakub Kacinski <[e-mail]>
Cc: Neal Cardwell <[e-mail]>
Cc: Paolo Abeni <[e-mail]>
Cc: Alice Ryhl <[e-mail]>
Cc: Stehen Rothwell <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/rbtree.h

···
 /* 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 *);
-extern struct rb_node *rb_first(const struct rb_root *);
+
+/*
+ * This function returns the first node (in sort order) of the tree.
+ */
+static inline struct rb_node *rb_first(const struct rb_root *root)
+{
+	struct rb_node	*n;
+
+	n = root->rb_node;
+	if (!n)
+		return NULL;
+	while (n->rb_left)
+		n = n->rb_left;
+	return n;
+}
 extern struct rb_node *rb_last(const struct rb_root *);
 
 /* Postorder iteration - always visit the parent after its children */

lib/rbtree.c

···
 }
 EXPORT_SYMBOL(__rb_insert_augmented);
 
-/*
- * This function returns the first node (in sort order) of the tree.
- */
-struct rb_node *rb_first(const struct rb_root *root)
-{
-	struct rb_node	*n;
-
-	n = root->rb_node;
-	if (!n)
-		return NULL;
-	while (n->rb_left)
-		n = n->rb_left;
-	return n;
-}
-EXPORT_SYMBOL(rb_first);
-
 struct rb_node *rb_last(const struct rb_root *root)
 {
 	struct rb_node	*n;

rust/helpers/rbtree.c

···
 {
 	rb_link_node(node, parent, rb_link);
 }
+
+struct rb_node *rust_helper_rb_first(const struct rb_root *root)
+{
+	return rb_first(root);
+}