kobject: Introduce kset_find_obj_hinted.

One call chain getting to kset_find_obj is:
  link_mem_sections()
    find_mem_section()
      kset_find_obj()

This is done during boot.  The memory sections were added in a linearly
increasing order and link_mem_sections tends to utilize them in that
same linear order.

Introduce a kset_find_obj_hinted which is passed the result of the
previous kset_find_obj which it uses for a quick "is the next object
our desired object" check before falling back to the old behavior.

Signed-off-by: Robin Holt <holt@sgi.com>
To: Robert P. J. Day <rpjday@crashcourse.ca>
Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 41 insertions, 0 deletions

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 7950a37a7146..8f6d12151048 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -191,6 +191,8 @@ static inline struct kobj_type *get_ktype(struct kobject *kobj)
 }
 
 extern struct kobject *kset_find_obj(struct kset *, const char *);
+extern struct kobject *kset_find_obj_hinted(struct kset *, const char *,
+                                                struct kobject *);
 
 /* The global /sys/kernel/ kobject for people to chain off of */
 extern struct kobject *kernel_kobj;
diff --git a/lib/kobject.c b/lib/kobject.c
index f07c57252e82..82dc34c095c2 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -746,17 +746,56 @@ void kset_unregister(struct kset *k)
  */
 struct kobject *kset_find_obj(struct kset *kset, const char *name)
 {
+        return kset_find_obj_hinted(kset, name, NULL);
+}
+
+/**
+ * kset_find_obj_hinted - search for object in kset given a predecessor hint.
+ * @kset: kset we're looking in.
+ * @name: object's name.
+ * @hint: hint to possible object's predecessor.
+ *
+ * Check the hint's next object and if it is a match return it directly,
+ * otherwise, fall back to the behavior of kset_find_obj().  Either way
+ * a reference for the returned object is held and the reference on the
+ * hinted object is released.
+ */
+struct kobject *kset_find_obj_hinted(struct kset *kset, const char *name,
+                                     struct kobject *hint)
+{
         struct kobject *k;
         struct kobject *ret = NULL;
 
         spin_lock(&kset->list_lock);
+
+        if (!hint)
+                goto slow_search;
+
+        /* end of list detection */
+        if (hint->entry.next == kset->list.next)
+                goto slow_search;
+
+        k = container_of(hint->entry.next, struct kobject, entry);
+        if (!kobject_name(k) || strcmp(kobject_name(k), name))
+                goto slow_search;
+
+        ret = kobject_get(k);
+        goto unlock_exit;
+
+slow_search:
         list_for_each_entry(k, &kset->list, entry) {
                 if (kobject_name(k) && !strcmp(kobject_name(k), name)) {
                         ret = kobject_get(k);
                         break;
                 }
         }
+
+unlock_exit:
         spin_unlock(&kset->list_lock);
+
+        if (hint)
+                kobject_put(hint);
+
         return ret;
 }