MINOR: ebtree: implement eb32sc_lookup_ge_or_first()

In the scheduler we always have to loop back to the beginning after
we don't find the last entry, so let's implement this in a new lookup
function instead. The resulting code is slightly faster, mostly due
to the fact that there's much less inlined code in the fast path.

diff --git a/ebtree/eb32sctree.c b/ebtree/eb32sctree.c
index 559c6a628a12fc1547506111592eb08d806ba632..4f48d58358a963f8f8b8612e7f1182df6338aebc 100644 (file)
--- a/ebtree/eb32sctree.c
+++ b/ebtree/eb32sctree.c
@@ -323,6 +323,97 @@ REGPRM2 struct eb32sc_node *eb32sc_lookup_ge(struct eb_root *root, u32 x, unsign
        //}
 }
 
+/*
+ * Find the first occurrence of the lowest key in the tree <root> which is
+ * equal to or greater than <x>, matching scope <scope>. If not found, it loops
+ * back to the beginning of the tree. NULL is returned is no key matches.
+ */
+REGPRM2 struct eb32sc_node *eb32sc_lookup_ge_or_first(struct eb_root *root, u32 x, unsigned long scope)
+{
+       struct eb32sc_node *eb32;
+       eb_troot_t *troot;
+       struct eb_root *curr;
+
+       troot = root->b[EB_LEFT];
+       if (unlikely(troot == NULL))
+               return NULL;
+
+       while (1) {
+               if ((eb_gettag(troot) == EB_LEAF)) {
+                       /* We reached a leaf, which means that the whole upper
+                        * parts were common. We will return either the current
+                        * node or its next one if the former is too small.
+                        */
+                       eb32 = container_of(eb_untag(troot, EB_LEAF),
+                                           struct eb32sc_node, node.branches);
+                       if ((eb32->leaf_s & scope) && eb32->key >= x)
+                               return eb32;
+                       /* return next */
+                       troot = eb32->node.leaf_p;
+                       break;
+               }
+               eb32 = container_of(eb_untag(troot, EB_NODE),
+                                   struct eb32sc_node, node.branches);
+
+               if (eb32->node.bit < 0) {
+                       /* We're at the top of a dup tree. Either we got a
+                        * matching value and we return the leftmost node, or
+                        * we don't and we skip the whole subtree to return the
+                        * next node after the subtree. Note that since we're
+                        * at the top of the dup tree, we can simply return the
+                        * next node without first trying to escape from the
+                        * tree.
+                        */
+                       if ((eb32->node_s & scope) && eb32->key >= x)
+                               troot = eb_dotag(&eb32->node.branches, EB_LEFT);
+                       else
+                               troot = eb32->node.node_p;
+                       break;
+               }
+
+               if (((x ^ eb32->key) >> eb32->node.bit) >= EB_NODE_BRANCHES) {
+                       /* No more common bits at all. Either this node is too
+                        * large and we need to get its lowest value, or it is too
+                        * small, and we need to get the next value.
+                        */
+                       if ((eb32->node_s & scope) && (eb32->key >> eb32->node.bit) > (x >> eb32->node.bit))
+                               troot = eb_dotag(&eb32->node.branches, EB_LEFT);
+                       else
+                               troot = eb32->node.node_p;
+                       break;
+               }
+               troot = eb32->node.branches.b[(x >> eb32->node.bit) & EB_NODE_BRANCH_MASK];
+       }
+
+       /* If we get here, it means we want to report next node after the
+        * current one which is not below. <troot> is already initialised
+        * to the parent's branches.
+        */
+       for (eb32 = NULL; !eb32; troot = eb_root_to_node(curr)->node_p) {
+               if (eb_gettag(troot) != EB_LEFT) {
+                       curr = eb_untag(troot, EB_RGHT);
+                       continue;
+               }
+
+               /* troot points to the branch location we're attached to by the
+                * left above, set curr to the corresponding eb_root.
+                */
+               curr = eb_untag(troot, EB_LEFT);
+
+               /* and go down by the right, but stop at the root */
+               troot = curr->b[EB_RGHT];
+               if (!eb_clrtag(troot))
+                       break;
+
+               eb32 = eb32sc_walk_down_left(troot, scope);
+       }
+
+       if (!eb32)
+               eb32 = eb32sc_walk_down_left(root->b[EB_LEFT], scope);
+
+       return eb32;
+}
+
 /* Removes a leaf node from the tree if it was still in it. Marks the node
  * as unlinked.
  */

diff --git a/ebtree/eb32sctree.h b/ebtree/eb32sctree.h
index 2999252cac5b03a205706d66e8b096927d1df625..d0dc31b71a7900a86c597d8e3d8f42379f8a6eb3 100644 (file)
--- a/ebtree/eb32sctree.h
+++ b/ebtree/eb32sctree.h
@@ -55,6 +55,7 @@ struct eb32sc_node {
  * in eb32sctree.c, which simply relies on their inline version.
  */
 REGPRM2 struct eb32sc_node *eb32sc_lookup_ge(struct eb_root *root, u32 x, unsigned long scope);
+REGPRM2 struct eb32sc_node *eb32sc_lookup_ge_or_first(struct eb_root *root, u32 x, unsigned long scope);
 REGPRM2 struct eb32sc_node *eb32sc_insert(struct eb_root *root, struct eb32sc_node *new, unsigned long scope);
 void eb32sc_delete(struct eb32sc_node *node);